Method of differentiating stem cells

ABSTRACT

The present disclosure provides methods of generating germ layers from stem cells comprising culturing the stem cells in a culture medium having an osmolality less than 340 mOsm/kg. The present disclosure also includes a method to generate different cell lineages from the germ layers as well as to detect them by immunological methods. The present disclosure further provides methods for the generation, isolation, cultivation and propagation of committed progenitor cells and for the production of differentiated cells from the three germ layers. The present disclosure also provides culture media for use in inducing the three germ layers.

RELATED APPLICATIONS

This application claims the benefit of priority of U.S. provisional applications No. 61/354,947 filed Jun. 15, 2010 and No. 61/251,130 filed Oct. 13, 2009, the contents of which are incorporated herein by reference in their entirety.

FIELD OF THE DISCLOSURE

The disclosure relates to methods of differentiating stem cells into germ layers and further into cell lineages. The disclosure also relates to media for said differentiation.

BACKGROUND OF THE DISCLOSURE

Human embryonic stem (ES) cells are pluripotent cells isolated from developing blastocysts. Induced pluripotent stem cells (iPS cells) are pluripotent cells originally isolated from somatic cells of the body reprogrammed by genetic and non-genetic approaches (for review see Amabile and Meissner, 2009). ES cells as well as iPS cells serve as an excellent in vitro system for studying differentiation events and as unlimited source for generating various specialized cell types in large quantities for basic research, drug screening and regenerative therapeutic applications.

Protocols to induce a certain germ layer cell type and subsequent definitive tissue types from human pluripotent stem cells, which includes human embryonic stem cells and induced pluripotent stem cells, are numerous, diverse and currently not standardized. They commonly involve differentiation using 3 major categories of protocols (for a review see Murry and Keller, 2008):

-   -   1. Based on co-culture of pluripotent stem cells with other cell         types such as feeder cells (e.g. D'Amour et al., 2005, Perrier         et al., 2005) or a somatic cell type (e.g. induction of         cardiomyocytes via co-culture with murine endoderm-like cell         lines (Mummery et al., 2007)); in medium conditioned by the         feeder cells, which induces a certain germ layer fate (Schulz et         al., 2003) or alternatively with the addition of factors         (D'Amour et al., 2005);     -   2. Based on adherent culture as monolayers with or in the         absence of serum and including the addition of morphogens (Nat         et al., 2007; Chambers et al., 2009);     -   3. Based on the formation of 3-D aggregates called embryoid         bodies (EBs). Cells in the EBs are multipotential, with the         propensity to develop into cells of any of the 3 germ layers         (endoderm, mesoderm or ectoderm) (Odorico et al., 2001). Usually         morphogens are also added either directly at the time of EB         formation to serve as inductive cue or at a later time-point         (e.g. after plating of the EBs) to selectively support survival         of the desired cell lineage (see embryonic stem cell protocols).

The major disadvantages of these protocols can be summarized as follows. The protocols are specific to each lab and are very operator and lab dependent making these protocols very difficult to transfer and reproduce in other labs without a huge investment in time and effort. Media formulations used in the 3 different categories of protocols above consist of a variety of media components, additives, supplement mixtures that are not consistent between labs and protocols. Detailed lists of the individual components in culture medium and their working concentrations are very often not available especially when pre-mixed supplements from commercial vendors are used.

The cultures derived from pluripotent stem cells even under the most defined conditions, are inherently heterogeneous, consisting of cell types of different lineages and at different stages of development. Heterogeneity may be explained by intrinsic cell-to-cell signaling and the variations in the time points used when manipulating the cells in some of the protocols. One solution that has been applied to increase the percentages of the desired cell type that are being induced is the use of morphogens like cytokines or growth factors as addition to the medium. These can be very costly and variable depending on the source.

Another common approach to control for heterogeneity is the use of selection strategies to obtain the desired cell types, such as mechanical selection or promotion of selective survival using certain media supplements and factors. Mechanical selection can be very tedious and also hardly gives rise to an entirely pure population of desired cell types. A major drawback of using certain supplements for the induction of cell types (e.g. N2 supplement for neural induction) is the interference with cell survival at later stages of the protocol when actual progenitor cells are isolated (Dhara et al., 2008).

Another disadvantage of many protocols is the amount of time it takes to obtain a pure differentiated cell population, especially when the protocol is multi-stepped and includes selection strategies as described above. The entire procedure may take up to several weeks.

Differentiated cell types derived from human pluripotent stem cells are the object of therapeutic approaches such as cell transplantations. Current research aims are focusing on the removal of animal derived proteins from human pluripotent stem cell cultures and differentiated lineages (Mallon et al., 2006). In many current protocols, so-called feeder cells used for the induction of germ layers are commonly derived from mouse tissues. In addition, differentiation of EBs especially into mesoderm often involves the use of fetal bovine serum in culture media, which is a non-characterized animal derived product.

Cell plating densities in monolayer cultures are often not well defined in many protocols and might influence the percentages of the desired cell types induced due to cell intrinsic signaling as described above. Early induction events may also be potentially influenced using differentiation protocols based on EB formation, which deal with variability in EB size and shape.

There is some evidence in the literature that the osmolality of the culture medium influences cell proliferation, survival and differentiation. For example, the osmolality of mTeSR™ medium was adjusted to a higher osmolality of 340 mOsm/kg compared to more standard osmolality of 290-330 mOsm/kg used in most cell culture media to better maintain the undifferentiated state of human ES cells (Ludwig et al., 2006). On the other hand, differentiated cell types such as primary neurons isolated from the CNS survive better in medium with low osmolality (230-280 mOsm/kg) compared to standard osmolality (Brewer et al., 1993; Brewer and Price 1996; Kivell et al., 2000). The available information suggests that a specific osmolality is either effective for maintaining cells in the undifferentiated state, promoting survival or maintaining already differentiated cells or mature cells in the differentiated state.

The lack of standardization of protocols for the differentiation of pluripotent stem cells has also been discussed widely in the literature (for a review see Sanchez-Pernaute and Sonntag, 2006).

Human ES cells are able to give rise to neural tissue in vitro either

-   -   1. Directed by an activity inherent to certain embryonic         fibroblast cells of murine or human origin. This activity is         referred to as stromal derived inducing activity or SDIA         (Perrier et al., 2004, Sonntag et al., 2007);     -   2. Spontaneously under adherent conditions as monolayers as         clumps or single cells and with the addition of supplements such         as N2 and B27 (Nat et al., 2007) or directed by addition of         morphogens (Osafune et al., 2007);     -   3. Spontaneously as an aggregated mass of differentiating cells         known as embryoid bodies (EBs), which is believed to occur         because of the presence of inductive factors inside of the EB         mimicking the events taking place in the early embryo. These EBs         contain cells of all three germ layers, including neuronal cells         of the ectodermal lineage (Odorico et al., 2001, Zhang et al.,         2001, Yan et al., 2005).

To date, all three of the foregoing methods of inducing neuroectoderm are inefficient and lead to heterogeneous populations of cells, many of which are non-neural.

However, higher efficiencies in neural/neuronal differentiation were achieved when human embryonic stem cells (hESCs) were exposed to morphogens like retinoic acid (Schuldiner et al., 2001), Fgf2 (Zhang et al., 2001), conditioned medium (Schulz et al., 2003; Shin et al., 2006), bone morphogenetic protein (BMP) inhibitors (Itsykson et al., 2005, Gerrard et al., 2005, Sonntag et al., 2007) or SMAD signaling inhibitors such as SB431542 (Chambers et al., 2009; Kim et al., 2010).

Although these protocols increase the emergence of neural cells, a subsequent selection of neural cells from this mixture had to be utilized in a majority of these protocols in order to obtain relatively pure populations of neuronal cells from differentiating cultures of ES cells. In vitro, early emerging neural progenitor cells are morphologically distinct from other cell types and are characterized by the formation of radially organized columnar epithelial cells termed “neural rosettes” (Zhang et al. 2001, 2005; Elkabetz et al., 2008). These structures comprise cells expressing early neuroectodermal markers such as Pax6 and Sox1 and are capable of differentiating into various region-specific neuronal and glial cell types in response to appropriate developmental cues (Yan et al., 2005, Perrier et al. 2004; Li et al. 2005). Over time in culture, the Pax6 positive cells down-regulate Pax6 expression and maintain Sox1 expression. However, they also begin to express Nestin. Similar protein expression profiles are observed in in vivo neural development when comparing neural precursors at the neural plate stage versus neural precursors emerging after neural tube closure (Jessell 2000). Currently, Nestin and Sox1 protein co-expression as well as formation of “neural rosettes” are considered a reliable criterion for the detection of neural progenitor cells (Elkabetz et al., 2008; Elkabetz and Studer 2009; Koch et al., 2009; Peh et al. 2009).

The controlled differentiation of human pluripotent cells into pure or highly enriched population neural progenitor cells and subsequent differentiation of these cells into the 3 cell types of the central nervous system (CNS): neurons, astrocytes and oligodendrocytes without any additional selection procedure would be highly desirable in the field since all these cell populations would provide real advantages for basic and applied studies of CNS development and disease.

To summarize, the field is lacking a standardized media formulation(s) and protocol(s) to induce the 3 germ layers and subsequently more specialized cell types derived thereof in a short period of time. The field also suffers from the lack of standardized protocols which are easy to reproduce in different labs and operator-dependent.

SUMMARY OF THE DISCLOSURE

The present inventors have addressed some of the major limitations in the field of pluripotent stem cell differentiation by developing media formulation(s) that allow one to obtain the desired differentiated cell type in a selective and standardized manner. The present inventors have shown that early induction of the 3 germ layers: mesoderm, ectoderm and endoderm from undifferentiated pluripotent stem cells, can be biased by manipulating the osmolality of the culture medium. Such media allows a morphogen-, serum- and feeder-free system that generates pure populations of germ layer progenitor cells.

Accordingly, the present disclosure provides a method of generating a population of germ layer progenitor cells comprising culturing stem cells in culture media with an osmolality of 260 to 340 mOsm/kg and allowing the cells to differentiate into germ layer progenitor cells.

In an embodiment, the present disclosure provides a method of generating a population of germ layer progenitor cells comprising:

(a) dissociating pluripotent stem cells into clusters or single cells;

(b) culturing the dissociated cells from a) in culture media with an osmolality of 260 to 340 mOsm/kg; and

(c) dissociating the cells of b) and plating the cells onto coated culture dishes and culturing for at least 1 day in the culture media to produce germ layer progenitor cells.

In one embodiment, culturing the dissociated cells in b) comprises culturing the dissociated cells from a) in a microwell device for about 24 hours to form aggregates and continuing the culture in the microwell device for more than 24 hours in the culture media followed by releasing the aggregates and adhering onto coated culture dishes and culturing in the culture media for at least 1 day. In one embodiment, the aggregates are cultured in the microwell device for up to 14 days, optionally 5-6 days, prior to releasing the aggregates and adhering onto the coated culture dishes. In another embodiment, the aggregates are cultured in the microwell device for up to 11 days.

In another embodiment, culturing the dissociated cells in b) comprises culturing the dissociated cells from a) in the culture media in a microwell device for about 24 hours to form aggregates, releasing the aggregates from the microwell device, followed by culturing the released aggregates in suspension in the culture media for at least 1 day, dissociating and adhering the aggregates onto coated culture dishes and culturing in the culture media for at least 1 day. In one embodiment, the cells are cultured in suspension for up to 14 days, optionally 5-6 days, before dissociating and adhering the aggregates onto coated culture dishes.

In yet another embodiment, culturing the dissociated cells in b) comprises culturing the dissociated cells from a) in suspension in the culture media for at least 1 day followed by dissociating the cells and adhering onto coated culture dishes and culturing in the culture media for at least 1 day. In one embodiment, the cells are cultured in suspension for up to 14 days, optionally 5-6 days, prior to dissociating and adhering onto the coated culture dishes.

In a further embodiment, culturing the dissociated cells in b) comprises adhering the dissociated cells from a) onto coated culture dishes and culturing for at least 3 days in the culture media. In one embodiment, the cells are cultured on the coated culture dishes for up to 14 days in the culture media, optionally 5-6 days. In another embodiment, the adhered cells are cultured on feeders.

In an embodiment, the culture media comprises Dulbecco's minimal essential medium and optionally, further comprises vitamins, trace elements, selenium, insulin, lipids, b-mercaptoethanol, non-essential amino acids, antibiotics, bFGF, B27, N2 or mixtures thereof. In another embodiment, the culture media comprises the components as shown in Table 2.

In one embodiment, the stem cells are mammalian pluripotent stem cells, optionally, human pluripotent stem cells. In another embodiment, the pluripotent stem cells are induced pluripotent stem cells or embryonic stem cells. In yet another embodiment, the germ layer is ectodermal, endodermal and/or mesodermal.

In one embodiment, the aggregates or clusters comprise embryoid bodies. In an embodiment, the embryoid bodies comprise 500 to 20,000 cells.

In one embodiment, the culture medium is 260 to 280 mOsm/kg for use in inducing ectodermal progenitor cells when the dissociated cells are first cultured in the microwell device and/or in suspension. In another embodiment, the osmolality of the culture medium is 270 to 320 m mOsm/kg for use in inducing ectodermal progenitor cells when the dissociated cells are plated directly onto coated culture dishes.

Also provided herein is a method of maintaining single neural progenitor cells in culture media with an osmolality of 260-340 mOsm/kg comprising generating ectodermal progenitor cells according to the methods described herein; dissociating the ectodermal progenitor cells from the cultures; plating and culturing said progenitor cells in the culture media for at least 1 day. In one embodiment, the osmolality is about 270 mOsm/kg. In another embodiment, the culture media comprises bFGF. In yet another embodiment, the progenitor cells are plated and cultured for at least 4 days. In a further embodiment, the ectodermal progenitor cells are further differentiated to form neurons, oligodendrocytes or astrocytes.

In another embodiment, the osmolality of the culture media is above 280 mOsm/kg, optionally 290-340 mOsm/kg, for inducing endodermal and/or mesodermal progenitor cells when the dissociated cells are first cultured in the microwell device and/or in suspension. In another embodiment, the osmolality of the culture medium is above 320 mOsm/kg, optionally 320 to 340 mOsm/kg, for inducing endodermal and/or mesodermal progenitor cells when the dissociated cells are plated directly onto coated culture dishes.

Also provided herein is a method of maintaining single mesodermal and/or endodermal progenitor cells in culture media with an osmolality of 290-340 comprising generating mesodermal and/or endodermal progenitor cells according to the methods described herein; dissociating the mesodermal and/or endodermal progenitor cells from the adhered cultures; and plating and culturing said progenitor cells. In an embodiment, the mesodermal and endodermal progenitor cells are further differentiated to form mesenchymal stem cells, chondrocytes, cardiomyocytes, hematopoietic stem cells, skeletal muscle cells, pancreatic cells or liver cells.

Also provided herein are culture media compositions useful for inducing germ layer differentiation and screening assays for agents that can modulate the differentiation of the cells or for primary or secondary screens of the cells generated by the methods described herein.

Other features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating preferred embodiments of the disclosure are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will now be described in relation to the drawings in which:

FIG. 1 shows human embryonic stem cells cultured on day 5 of culture on BD Matrigel™ (H9 p51) Magnification: 2× (left), 10× (right).

FIG. 2 shows human embryonic stem cells cultured on mouse fibroblast cells (MEFs) on day 4 of culture. Magnification: 2×.

FIG. 3 shows the morphology of undifferentiated pluripotent human ESCs (left side) and of a culture showing signs of differentiation (right side). Top: magnification 2×, bottom: 10×.

FIG. 4 shows EB formation in AggreWell: single cell suspensions are distributed in a single well of an AggroWell™400 plate. Each microwell holds 2000 cells. Magnification: 2× (left) and 10× (right).

FIG. 5 shows scraped EBs after 1 day of suspension culture. Magnification: 2× (left) and 10× (right).

FIG. 6 shows EBs after 24 h incubation in AggreWell™ 400 plate. EBs formed via forced aggregation in the AggreWell™ 400 plate were applied onto cell strainer to remove single cells. 2×, 10× and 40× magnification.

FIG. 7 shows neural rosettes induced from human embryonic stem cells at day 5 in adherent culture conditions. Media used were mTeSR®1-F 270 mOsm/kg+1× B27/N2A (upper row) and mTeSR®1-F 320 mOsm/kg+1× B27/N2A (lower row). Arrows point towards rosette structures. Left column: magnification 2×, right column: magnification 10×.

FIG. 8 shows neural rosettes induced in 3 different media in EB based conditions in AggreWell™ 400. Upper row: mTeSR®1-F 260 mOsm/kg; middle row: mTeSR®1-F 270 mOsm/kg; lower row: mTeSR®1-F 280 mOsm/kg. Arrows point towards rosette structures. Left column: magnification 2×, right column: magnification 10×.

FIG. 9 shows average rosettes counts of experiments where EBs were induced and cultured in mTeSR®1-F 260 mOsm/kg (33.3%); mTeSR®1-F 270 mOsm/kg (40.6%) or mTeSR®1-F 280 mOsm/kg (30%).

FIG. 10 shows the morphology of attached EBs after 5 days of suspension culture in mTeSR®1-F 270 mOsm/kg (upper row, left 2 pictures); mTeSR®1-F 290 mOsm/kg (upper row, right 2 pictures); mTeSR®1-F 320 mOsm/kg (lower row, left 2 pictures) or mTeSR®1-F 340 mOsm/kg (lower row, right 2 pictures). Magnifications: 2× (left pictures in each condition) and 10× (right pictures in each condition).

FIG. 11 shows attached EBs after 3 days. Immunocytochemical staining for Nestin (left column) and Sox1 (right column). The area of the picture where there is Sox1 expression is marked off (white line). EBs were formed either in mTeSR®1-F 270 mOsm/kg (upper row) or mTeSR®1-F 340 mOsm/kg (lower row). The area of cells expressing Sox1 is clearly larger in cells induced in mTeSR®1-F 270 mOsm/kg compared to cells induced in or mTeSR®1-F 340 mOsm/kg. Magnification 20×.

FIG. 12 shows the average rosettes counts of individual experiments where EBs were induced and cultured in mTeSR®1-F 320 mOsm/kg (13%) or mTeSR®1-F 340 mOsm/kg (7.9%).

FIG. 13 shows pictures of cell morphologies during the selective neural progenitor dissociation procedure using 1×PBS (Ca, Mg free), pH 7.4. Upper row, left picture: rosette colonies before dissociation. Upper row, middle: during dissociation (20 min), upper row, right picture: during dissociation (40 min). Lower row, left picture: during dissociation (60 min), lower row, middle: after dissociation (when neural progenitor cells were lifted off by trituration (90 min), lower row, right: cells that remained on dish after trituration. Magnifications: all, except lower row left and middle: 10×; lower row left and middle: 2×.

FIG. 14 shows neural progenitor cells plated after selective dissociation with 1×PBS (Ca, Mg free), pH 7.4 at day 3 (upper row), day 6 (middle row) and day 12 (lower row). Left column: mTeSR®1-F 270 mOsm/kg and right column: mTeSR®1-F 340 mOsm/kg. Magnification: left: 4×, right: 10×.

FIG. 15 shows neural progenitor cells 6 days after selective dissociation with PBS. Cells were plated and immunocytochemistry was performed using the Nestin antibody and the Sox1 antibody (right column). The left column represents the same cells stained with DAPI as nuclei-counterstaining. Cells were originally induced and grown in mTeSR®1-F 270 mOsm/kg (upper row) or mTeSR®1-F 340 mOsm/kg (lower row). Clearly, there are fewer cells stained with both antibodies present in the neural progenitor cells obtained in mTeSR®1-F 340 mOsm/kg. Magnification 20×.

FIG. 16 shows manually selected rosette colonies from EBs formed, grown and attached in mTeSR®1-F 270 mOsm/kg, 2 days after selection. Magnification 10×.

FIG. 17 shows neural progenitor cells were passaged and pictures were taken at 2 days after attachment (left) or 5 days after attachment (right). Magnification 10×.

FIG. 18 shows neurons stained with anti TUJ1 antibody derived from neural progenitor cells cultured in mTeSR®1-F 270 mOsm/kg (left) but not in mTeSR®1-F 340 mOsm/kg (right). TUJ1 and Sox1 antibody staining is displayed with separate arrows. Sox1 is not expressed in neurons. Magnification 20×.

FIG. 19 shows human embryonic stem cell line H1 at day 5 of passage 39 (A) and human induced pluripotent stem cell line 4D1 at day 5 of passage 33 (B) cultured on BD Matrigel™. Magnification: 2× (A, B) and 10× (C).

FIG. 20 shows human embryonic stem cell line colonies (H9) at approximately 70% confluency at day 5 of culture (A, B) after passage as single cell suspensions and one day after H9 were re-plated at a density of 2×10⁴ per cm² (C). Magnifications 2× (A), 10× (B and C).

FIG. 21 shows EBs generated from 4D1 pluripotent stem cells inside the microwells of an AggreWell™800 plate after 24 hours and before harvest (A and B). EBs harvested from AggreWell™800 after 2 days (C) and 4 days (D and E) in suspension culture. Magnifications: 4× (A), 10× (B,E), 2× (C,D).

FIG. 22 shows representative images of neural rosettes observed in the EBs attached to poly-L-ornithine/laminin plates at day 3 (A-D). The attached EBs of ˜2000 cells per EB shown here were previously generated from human induced stem cell line 4D1 using AggreWell™800. Magnifications: 2× (A), 10× (B-D).

FIG. 23 shows neural rosettes (arrows for a few examples) observed in the EBs attached to poly-L-ornithine/laminin plates generated from cell lines 4D1 (A-D) and H9 (E-H). Attached EBs containing 2000 cells per EB (A-D) and 5000 cells per EB (E-H) cultured in mTeSR®1-F 270 mOsm/kg (A,B,E,F) or mTeSR®1-F 340 mOsm/kg (C,D,G,H). Scoring results are also indicated as % within the corresponding images. Magnifications 2× (A,C,E,G), 10× (B,D,F,H)

FIG. 24 shows attached EBs 1 day after plating of different sized EBs previously generated from H9 human embryonic stem cells. The different size of EBs are as follows: 500 cells per EB (A and B), 1000 cells per EB (C and D) and 2000 cells per EB (E and F). Magnifications 2× left (A, C and E), 10× right column (B, D and F).

FIG. 25 shows the morphology at day 2 of EBs harvested from the microwell device and plated on poly-L-orthinine/laminin coated plates. The scoring results are indicated as % within the corresponding images. EBs generated in mTeSR®1-F 270 mOsm/kg (A, B and C) and EBs generated in mTeSR®1-F 340 mOsm/kg (D, E and F). EBs sizes tested were EBs of 2000 cells per EB (C and F) and 500 cells per EB (A, B, D and E). Magnification: 2× (A,C,D,F) and 10× (B,E).

FIG. 26 shows EBs of various sizes inside the microwells of AggreWell™800 at day 5 before harvest and plating of the EBs. The following EB sizes are shown: EBs of a size of 2000 cells per EB (A and B), EBs of a size of 5000 cells per EB (C and D), EBs of a size of 10000 cells per EB (E and F), EBs of a size of 15000 cells per EB (G) and EBs of a size of 20000 cells per EB (H). Magnification:4× (A,C,E,H), 10× (B,D,F,G);

FIG. 27 shows EBs at various sizes harvested from the microwell device and after 1 one day of plating on poly-L-ornithine/laminin plates: The following EB sizes are shown: EBs of a size of 2000 cells per EB (A,B), 5000 cells per EB (C,D), 10000 cells per EB (E,F), 15000 cells per EB (G,H) and 20000 cells per EB (I,J). Magnification: 2× (A,C,E,G,I) and 10× (B, D, F, H, J).

FIG. 28 shows the morphology of EBs generated in mTeSR®1-F 270 mOsm/kg (A-D) and mTeSR®1-F 340 mOsm/kg (E-H) and plated on poly-D-ornithine/laminin at day 2. The following EB sizes are shown: EBs of a size of 2000 cells per EB (A,B,E,F) and EBs of a size of 5000 cells per EB (C,D,G,H). Magnification: 2× (A,C,E,G) and 10× (B,D,F,H).

FIG. 29 shows attachment of EBs generated in media with different osmolalities and then plated on poly-L-ornithine/laminin coated plates in the same media after 2 days. Attached EBs which were previously generated in mTeSR®1-F 270 mOsm/kg (A,B), mTeSR®1-F 320 mOsm/kg (C,D), .mTeSR®1-F 340 mOsm/kg (E,F), mTeSR®1-F 400 mOsm/kg (G,H) and mTeSR®1-F 450 mOsm/kg (I,J). Magnifications: left 2× (A,C,E,G,I), and 10× (B,D,F,H,J).

FIG. 30 shows the scoring results for attached EBs generated in media with different osmolalities (mTeSR®1-F 270 mOsm/kg; mTeSR®1-F 320 mOsm/kg, mTeSR®1-F 340 mOsm/kg and mTeSR®1-F 400 mOsm/kg) after 2 days. The cultures containing mTeSR®1-F 450 mOsm/kg were visually inspected for presence of rosettes on day 1.

FIG. 31 shows EBs 3 days after attachment. EBs were previously generated from human embryonic stem cell line H9, which had been passaged as single cell suspensions for 4 passages (p51-p55) in mTeSR®1-F 270 mOsm/kg (A) or mTeSR®1-F 340 mOsm/kg (B). Magnification 2×.

FIG. 32 shows H9 cells at 5 days of passage 52 prior to EB formation (A-D). Circled areas indicate differentiated areas of the colonies at low magnification (A,C) and the same areas at high magnification (B,D). EBs previously formed in mTeSR®1-F 270 mOsm/kg are shown here 2 days after attachment on poly-L-ornithine/laminin coated plates (E,F). Scoring results are indicated as % within the corresponding images. EBs previously formed in mTeSR®1-F 340 mOsm/kg are shown here 2 days after attachment on poly-D-ornithine/laminin coated plates (G,H). Magnifications: 2× (A,C,E,G) and 10× (B,D,F,H).

FIG. 33 shows attached EBs generated from hESC line H7 p38 1 day after plating. EBs containing 5000 cells per EB were generated in mTeSR®1-F 270 mOsm/kg (A, B) or in mTeSR®1-F 340 mOsm/kg (C, D). Magnifications 2× (A, C, D), 10× (B).

FIG. 34 shows attached EBs generated from hESC line H9 p44 2 days after plating. EBs containing 2000 cells per EB were generated in Knockout™-D-MEM 270 mOsm/kg (A, B) or in Knockout™-D-MEM 340 mOsm/kg (C, D). Scoring results are indicated as “%” within the corresponding images. Magnifications 2× (A, C), 10× (B, D).

FIG. 35 shows EBs with a size of 2000 cells per EB generated from hESC line H9 p44 at day 5 within the microwells of AggreWell™400 just before releasing and plating of the EBs (A, D). B, C, E, F show attached EBs 2 days after plating. EBs were generated in Neurobasal™ 270 mOsm/kg (A, B, C) or in Neurobasal™ 340 mOsm/kg (D, E, F). Scoring results are indicated as “%” within the corresponding images. Magnifications 2× (B, E), 4× (A, D) and 10× (C, F).

FIG. 36 shows attached EBs containing 500 (A, B, E, F), 2000 (C, D) and 5000 cells per EB (G, H) generated from hESC line H9 p41, p45 and p44 respectively, 3 days after plating. EBs were generated in mTeSR®1-F 270 mOsm/kg (BSA lot 2) (C, G), mTeSR®1-F 270 mOsm/kg (BSA lot 3) (A, B), mTeSR®1-F 340 mOsm/kg (BSA lot 2) (D, H) or in mTeSR®1-F 340 mOsm/kg (BSA lot 3) (E, F). Scoring results are indicated as “%” within the corresponding images. Magnification 2×.

FIG. 37 shows attached EBs containing 2000 (A, B), 5000 (C, D) and 10000 cells per EB (E, F) generated from hESC line H9 p44 and p53, 2 days after plating. G, H show attached EBs containing 2000 cells each generated from the hESC line H1 p59. All EBs were generated in mTeSR®1-F 270 mOsm/kg (BSA lot 2). Magnification 2× (A, C, E, G), 10× (B, D, F, H)

FIG. 38 shows attached EBs generated from hESC line H9 p52 2 days after plating. EBs containing 2000 cells per EB were generated in mTeSR®1-F 270 mOsm/kg (A, B) or in mTeSR®1-F 340 mOsm/kg (C, D). Scoring results are indicated as “%” within the corresponding images. Magnification 2× (A, C), 10× (B, D)

FIG. 39 shows attached EBs generated from hESC line H9 p64 2 days after plating. EBs containing 2000 cells per EB were generated in mTeSR®1-F 270 mOsm/kg (BSA lot 2) (A, B, E, F) or in mTeSR®1-F 340 mOsm/kg (C, D, G, H) using either AggreWell™400 (A-D) or AggreWell™800 (E-H). Scoring results are indicated as “%” within the corresponding images. Magnification 2× (A, C, E, G), 10× (B, D, F, H).

FIG. 40 shows attached EBs containing 2000 cells per EB generated from hESC line H9 p52 2 days after plating. EBs were generated in TeSR™2-F 270 mOsm/kg (containing HSA) (A, B) or in TeSR™2-F 340 mOsm/kg (containing HSA) (C, D). Scoring results are indicated as “%” within the corresponding images. Magnification 2× (A, C), 10× (B,D).

FIG. 41 shows attached EBs generated from hESC line H9 p52 6 days after culture in suspension culture (ULA dishes) followed by plating on coated dishes. EBs were generated in mTeSR®1-F 270 mOsm/kg (A), mTeSR®1-F 270 mOsm/kg supplemented with 20 ng/mL bFGF (B) or mTeSR®1-F 270 mOsm/kg supplemented with 20 ng/mL bFGF, 1% B27 and 1% N2A (C). D-F show attached EBs at 4 days after plating. These EBs were cultured in AggreWell™800 plates for 5 days prior to plating in either mTeSR®1-F 270 mOsm/kg supplemented with 1% N2A (D), mTeSR®1-F 270 mOsm/kg supplemented with 100 ng/mL FGF8 and 200 ng/mL SHH (E) or mTeSR®1-F 270 mOsm/kg supplemented with 1% B27 (F). Magnification 2× (A, B, C, D, F), 10× (E).

FIG. 42 shows attached EBs generated from hESC line H9 p36 and p42 at different days after plating. EBs containing 2000 cells per EB were generated in mTeSR®1-F 270 mOsm/kg. EBs shown in (A) were plated at day 1 after EB formation and are shown at day 3 after plating (a total of 4 days in culture). EBs shown in (B) were plated at day 1 after EB formation and are shown at day 5 after plating (a total of 6 days in culture). EBs shown in (C) were plated at day 2 after EB formation and are shown at day 1 after plating (a total of 3 days in culture). EBs shown in (D) were plated at day 2 after EB formation and are shown at day 5 after plating (a total of 7 days in culture). EBs shown in (E, F) were plated at day 3 after EB formation and are shown at day 3 after plating (a total of 6 days in culture). EBs shown in (G) were plated at day 4 after EB formation and are shown at day 2 after plating (a total of 6 days in culture). EBs shown in (H) were plated at day 5 after EB formation and are shown at day 2 after plating (a total of 7 days in culture). (I) shows a FACS plot of attached EBs plated at day 1 (0.77% positive cells) stained with antibodies for the neural marker Sox1. (J) shows a FACS plot of Sox1 positive cells of EBs plated at day 5 (35.21% positive cells; the left plots in both (I and J) represent the gating for live cells). Magnification 2× (A-E, G, H), 10× (F).

FIG. 43 shows attached EBs generated from hESC line H9 p36 and p42 at different days after plating. EBs containing 2000 cells per EB were generated in mTeSR®1-F 270 mOsm/kg. EBs shown in (A, B) were plated at day 7 after EB formation and are shown at day 2 after plating (a total of 9 days in culture). EBs shown in (C, D) were plated at day 8 after EB formation and are shown at day 2 after plating (a total of 10 days in culture). EBs shown in (E, F) were plated at day 11 after EB formation and are shown at day 2 after plating (a total of 13 days in culture). EBs shown in (G, H, I) were plated at day 11 after EB formation and are shown at day 5 after plating (a total of 16 days in culture). Circles in (G) mark rosettes structures, thin arrows in (H) mark neural progenitor cells and thick arrows in (I) mark mature neurons. Magnification 2× (A, C, E), 10× (B, D, F, G, H, I).

FIG. 44 shows attached EBs generated from hESC line H9 p38 3 days after plating on different surfaces. EBs containing 2000 cells per EB were generated in mTeSR®1-F 270 mOsm/kg. (A) shows EBs that were plated on dishes coated with Poly-L-ornithine and 1 μg/mL of laminin. (B) shows EBs that were plated on dishes coated with Poly-L-ornithine and 10 μg/mL of laminin. (C) shows EBs that were plated on dishes coated with Poly-L-ornithine and 20 μg/mL of laminin. Magnification 2×.

FIG. 45 shows neurospheres at day 1 after suspension culture for 5 days in ultra low adherence (ULA) dishes plates. Neurospheres were generated from attached EBs initially formed in mTeSR®1-F with an osmolality of 270 mOsm/kg alone (A) or in mTeSR®1-F with an osmolality of 270 mOsm/kg supplemented with 1% B27 (B) or in mTeSR®1-F with an osmolality of 270 mOsm/kg supplemented with 1% N2A (C). Arrows point towards neurons growing out and extending axons from the attached neurosphere.

FIG. 46 shows attached EBs at day 6 after plating. EBs were formed in mTeSR®1-F with an osmolality of 260 mOsm/kg (A-C) or mTeSR®1-F with an osmolality of 270 mOsm/kg (D-F) and were cultured for 13 days inside AggreWell™800. Neural rosettes are indicated with thick arrows and neurons with thin arrows in A-F. Magnification 10× (A, B, C, E, F), 4× (D).

FIG. 47 shows attached EBs generated from hESC line H9 p47 4 days after plating. hESCs were either cultured in hESC maintenance medium until EB formation (A) or were pre-conditioned for 24 hours in mTeSR®1-F 320 mOsm/kg (B). Then, EBs were generated in mTeSR®1-F 270 mOsm/kg and cultured in suspension culture (ULA dishes) for 5 days after which they were allowed to attach. Scoring results are indicated as “%” within the corresponding images. Magnification 2×.

FIG. 48 shows neural progenitor cells (NPCs), which were obtained from attached EBs which were dissociated by different methods. EBs had been previously generated from hESCs line H9 p47 in AggreWell™400 and mTeSR®1-F with an osmolality of 270 mOsm/kg. They were cultured in suspension culture (ULA dishes) for 5 days prior to plating of the EBs. NPCs shown in (A) were derived from attached EBs using cell dissociation buffer enzyme-free PBS based, 0.02% EDTA solution (B), 1 mg/mL Dispase (C), Accutase™ (D), Neurocult® Chemical Dissociation Kit (Mouse) (E) or 0.05% trypsin-EDTA (F). Magnification 10×.

FIG. 49 shows neural progenitor cells (NPCs), which were obtained from attached EBs which were dissociated using different dissociation methods at 3 days after plating and stained using immunocytochemistry (ICC) for NPC marker Sox1 (stains the nucleus of the cell) and Nestin (stains the cytoplasm of the cell; arrows in (C). NPCs in (A) have been derived from attached EBs dissociated using Accutase™. NPCs shown in (B) have been derived from attached EBs dissociated using HBSS. NPCs shown in (C) have been derived from EBs dissociated using D-PBS without Ca++ and Mg++. Magnification 20×.

FIG. 50 shows attached EBs containing 2000, 5000 and 10000 cells/EB generated from hESC lines H7 and H9 (passages 38 or 35, 36, 41, 45, respectively) at different days after plating. EBs were also released from AggreWell™800 plates at different time points. Attached EBs (5000 cells/EB at initial formation) shown in (A, B) were released and plated on day 5 and the picture is representative of the cell morphology at day 7 after plating. Attached EBs (10000 cells/EB at initial formation) shown in (C, D) were released and plated on day 5 and the picture is representative of the cell morphology at day 7 after plating. Attached EBs (2000 cells/EB at initial formation) shown in (E, F) were released and plated on day 11 and the picture is representative of the cell morphology at day 5 after plating. Attached EBs (10000 cells/EB at initial formation) shown in (G, H) were released and plated on day 6 and the picture is representative of the cell morphology at day 8 after plating. Magnification 2× (A, C, E, G), 10× (B, D, F, H).

FIG. 51 shows NPC 5 (A, B) or 6 days (C-I) after plating from dissociated attached EBs (described in FIG. 50). EBs were previously released at different days from AggreWell™800 plates. NPCs shown in (A, B) were dissociated on day 5 after attachment of EBs (2000 cells/EB) which were released from AggreWell™800 on day 8. NPCs shown in (C) were dissociated on day 8 after attachment of EBs (10000 cells/EB), which were released from AggreWell™800 on day 6. NPCs shown in (D, E, F) were dissociated on day 7 after attachment of EBs (5000 cells/EB), which were released from AggreWell™800 on day 5. NPCs shown in (G, H) were dissociated on day 7 after attachment of EBs (10000 cells/EB), which were released from AggreWell™800 on day 5. NPCs shown in (I) were dissociated on day 6 after attachment of EBs (5000 cells/EB), which were released from AggreWell™800 on day 5. Magnification 20× (A, D, G), 40× (B, C, E, F, H, I).

FIG. 52 shows NPC 4 days after they isolated from dissociated attached EBs and plated (represented in FIG. 50). EBs were released from AggreWell™800 plates at different days. NPCs shown in (A) were isolated on day 11 after attachment of EBs (2000 cells/EB), which were released from AggreWell™800 on day 7. (B) shows an immunocytochemical (ICC) staining of the same NPCs for the neuronal marker PSA-NCAM (arrows point towards positively stained lumina of rosette structures). (C) shows an ICC staining of the same NPCs for the neuronal rosette marker ZO-1, staining the lumen of the rosette specifically (arrows). NPCs shown in (D) were isolated on day 9 after attachment of EBs (2000 cells/EB), which were released from AggreWell™800 on day 9. (E) shows an ICC staining of the same NPCs for the neuronal marker Sox1 (circles mark some of the rosette structures present). (F) shows an ICC staining of the same NPCs for the neuronal marker Nestin (Nestin stains the cytoplasm as marked here by an arrow, all cells are positive). NPCs shown in (G) were isolated on day 7 after attachment of EBs (2000 cells/EB), which were released from AggreWell™800 on day 11. (H) shows an ICC staining of the same NPCs for the neuronal marker Nestin (all cells are positive). All stained cells are counter-stained in blue using DAPI. Magnification 10× (A, D, G), 20× (B, C, E, F, H).

FIG. 53 shows a chart, which summarizes the results from FIGS. 50-52 including a list of the age of NPCs at the end of passage 2 and the source of NPCs: 1. The day EBs were released from their microwell, 2. The day NPCs were isolated from attached EBs (shown in FIG. 50), 3. The total number of days at dissociation of attached EBs (shown in FIG. 50), 4. The number of cells per EB and 5. The day the picture of NPCs (shown in FIG. 51 or 52) was taken total, which equals the number of days in culture.

FIG. 54 shows attached EBs and the isolated NPCs, generated from hESC line H9 p65. EBs were formed in AggreWell™800 plates at a size of 2000 cells per EB. EBs were cultured in the plates for 12 days until they were released. (A-D) show attached EBs at day 4 after plating. (E-H) show NPCs 3 days after they have been isolated from attached EBs and were plated on 1, 5, 10 and 20 μg/ml laminin (E-H, respectively). (I-L) show the same NPCs 7 days after plating. Magnification 10×.

FIG. 55 shows NPCs shown in FIG. 54 stained with an antibody against TUJ-1 on day 3 when plated on 10 μg/ml laminin or 20 μg/ml laminin and on day 7 when plated on 1 μg/ml laminin or 5 μg/ml laminin (neurons can be identified by their bright appearance and the axons they are extending). Cells are counter-stained in blue using DAPI. Magnification 20×.

FIG. 56 shows attached EBs and the isolated NPCs generated from hESC line H9. EBs were generated in AggreWell™800 and were released and plated at day 11. The pictures of the attached EBs were taken at day 11 after attachment (A, B, D, E). NPCs were derived from these attached EBs and are shown on day 3 after plating (C, F). mTeSR®1-F 270 mOsm/kg (A-C) or mTeSR®1-F 340 mOsm/kg (D-F) were used for the formation of EBs, culture of the attached EBs and subsequent culture of NPCs. Magnification 2× (A, B, D, E), 10× (C, F).

FIG. 57 shows NPCs described in FIG. 56 stained with antibodies against the neural marker Nestin, the neuronal marker TUJ1 (A, B) and the neural marker Sox1 (C). Arrows in (A) and (B) mark regions with high density of Nestin positive cells (less in (B)). Many cells express Sox1. Magnification 20×.

FIG. 58 shows NPCs derived from hESC line H9 p36 and p41. EBs were formed at different sizes (2000, 5000 and 10000 cells/EB) in AggreWell™800 and released on day 5 or 7. NPCs were isolated from attached EBs at day 11 (for the 2000 cells/EB) or at day 7 (5000 and 10000 cells/EB). (A) shows NPCs isolated from EBs previously cultured in AggreWell for 7 days (2000 cells/EB), grown as attached EB-cultures for 11 days and then treated with HBSS on day 4 of culture. (B) shows NPCs on day 6 isolated from attached EBs at day 7 using HBSS; these EBs (10000 cells/EB) were previously cultured in AggreWell for 5 days. C) shows passage 2 NPCs on day 3 of culture after dissociation using HBSS of cells from (A). These NPCs were plated onto Poly-L-ornithine/laminin coated dishes. (D) shows passage 2 NPCs on day 1 of culture after dissociation using TrypIE of cells from (B). These NPCs were plated onto matrigel coated dishes. E) shows passage 3 NPCs on day 3 of culture after a dissociation using Trypsin of cells from (C). These NPCs were plated onto Poly-L-ornithine/laminin coated dishes. (F) shows passage 3 NPCs on day 4 of culture after dissociation using TrypIE of cells from (D). These NPCs were plated onto Poly-L-ornithine/laminin coated dishes. Magnification 10×.

FIG. 59 summarizes the results described in FIG. 58. (A) shows NPCs on day 5 of passage 1 stained for the neural marker musashi and with the rosette-marker ZO-1 (all cells are musashi positive, ZO-1 stains the lumen of the prominent rosette structures). (B) shows NPCs on day 6 of passage 1 (p1d6) stained for the neuronal marker TUJ-1 (arrows mark some axonal structures). Magnification 20×.

FIG. 60 shows attached EBs stained for the neural markers Pax6 (A, E) and Sox1 (B, F). (C, G) represent overlays of the two markers and (D, H) show DAPI-counter-stain of the cells. EBs containing 500 cells/EB were formed from hESC line H9 p63 in AggreWell™400 and were released and plated after 5 days. The induction medium mTeSR®1-F 270 mOsm/kg was used for the culture of attached EBs shown in (A-D) while mTeSR®1-F 340 mOsm/kg was used for the culture of attached EBs shown in (D-H). It can be seen from (A, C and D) compared to (E, G and H) that cells derived from EBs formed and cultured in mTeSR®1-F 270 mOsm/kg express more of the neural marker Pax6 and Sox1. Magnification 10×.

FIG. 61 shows attached EBs from various experiments and at different days after plating co-stained for the neural markers Pax6 and Sox1 (A), Sox1 and Nestin (B) and Sox1 and Nestin (C) to demonstrate abundance of neural progenitor cells. All cells co-express all 3 marker combinations, respectively. Magnification 10×.

FIG. 62 shows attached EBs from various experiments and at different days after plating co-stained for the neural markers Pax6 and the rosette marker ZO-1 (A), the neural marker Sox1 and the rosette marker ZO-1 (B) as well as the radial glia marker BLBP and the neural marker Nestin (C, D). All cells are double-positive in (A) and (B) and rosette structures in (C) and (D), are double-positive for Nestin and BLBP appearing bright in the picture. Magnification 10× (A, B), 20× (C, D).

FIG. 63 shows attached EBs 2 days after plating. EBs were generated from hESC line H9 p51 in mTeSR®1-F 270 mOsm/kg (A) or mTeSR®1-F 340 mOsm/kg (B, C). Narrow arrows in (A) point towards neural rosettes. Broad arrows in (B and C) point towards flat cells surrounding attached EBs. Note that no neural rosettes are present in these illustrations. Magnification 10×.

FIG. 64 shows a graph representing qPCR results (relative quantification (RQ value)) of Nestin (dark grey) and Sox1 (light grey) transcript expression in neural rosette cells and non-neural “flat” cells isolated from attached EBs at day 2 (described in FIG. 63) generated previously from H9 p52 hEScs in mTeSR®1-F 270 mOsm/kg or mTeSR®1-F 340 mOsm/kg, respectively.

FIG. 65 shows NPCs (H9; p36 cells) at passage 1 day 8 (p1d8) (A), p2d2 (B) and p3d3 (C). NPCs were derived from attached EBs on day 5 after plating (released from AggreWell at day 5). In passage 1 and 2 mostly NPCs were observed, while in passage 3 sub-populations of neurons emerged spontaneously. (D) shows cells in p1 stained for the neural marker Nestin and the neuronal marker TUJ-1. (E) shows cells in p3 stained for the neural marker Nestin and the neuronal marker TUJ-1. Arrows point towards axons extending from neurons. There are more neurons present in (E) than in (D). Magnification 10×.

FIG. 66 shows spontaneously differentiated neurons derived from NPCs co-stained for the pan-neuronal marker TUJ-1 (marked by short, thick arrows) (A) and the GABAergic neuron marker GABA (arrow) (B). (C) shows an overlap of TUJ-1 and GABA staining and shows that not all neurons are GABAergic neurons. The arrow in (B) and (C) marks a positive GABAergic neuron. (D) GFAP positive cells (thick arrows), indicating the presence of astrocytes can also be identified in spontaneously differentiated of NPCs. Neurons staining positive for TUJ-1 do not co-stain for GFAP (thin arrows). Magnification 40×.

FIG. 67 shows neural induction from hESC line H9 passage 55, passaged for 4 passages as single cell suspension. Adherent NPC cultures 7 days after neuroectoderm induction in mTeSR®1-F 270 mOsm/kg (A, D), mTeSR®1-F 270 mOsm/kg supplemented with 1% N2A, 1% B27 (B, E) or mTeSR®1-F 270 mOsm/kg supplemented with 2% B27 on matrigel. Magnification 2× (A-C), 10× (D-F).

DETAILED DESCRIPTION OF THE DISCLOSURE Methods of the Disclosure

Inducing Germ Layer Progenitor Cells

The present inventors have developed methods of inducing germ layer progenitor cells by culturing stem cells in media with controlled osmolality.

Accordingly, the present disclosure provides a method of generating a population of germ layer progenitor cells comprising culturing stem cells in culture media with an osmolality lower than 340 mOsm/kg, optionally in the range of 240-340 mOsm/kg or 260-340 mOsm/kg, and allowing the cells to differentiate into germ layer progenitor cells.

In an embodiment, the present disclosure provides a method of generating a population of germ layer progenitor cells comprising:

(a) dissociating pluripotent stem cells into clusters or single cells;

(b) culturing the dissociated cells from a) in culture media with an osmolality of 260 to 340 mOsm/kg; and

(c) dissociating the cells of b) and plating the cells onto coated culture dishes and culturing for at least 1 day in the culture media to produce germ layer progenitor cells.

In one embodiment, culturing the dissociated cells in b) comprises culturing the dissociated cells from a) in a microwell device for about 24 hours to form aggregates and continuing the culture in the microwell device for more than 24 hours in the culture media followed by releasing the aggregates and adhering onto coated culture dishes and culturing in the culture media for at least 1 day. Aggregates are optionally cultured inside the microwell device for 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or more days prior to releasing and adhering onto the coated culture dishes.

In another embodiment, culturing the dissociated cells in b) comprises culturing the dissociated cells from a) in the culture media in a microwell device for about 24 hours to form aggregates, releasing the aggregates from the microwell device, followed by culturing the released aggregates in suspension in the culture media for at least 1 day, dissociating and adhering the aggregates onto coated culture dishes and culturing in the culture media for at least 1 day. Aggregates are optionally cultured in suspension for 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or more days prior to releasing and adhering onto the coated culture dishes.

In yet another embodiment, culturing the dissociated cells in b) comprises culturing the dissociated cells from a) in suspension in the culture media for at least 1 day followed by dissociating the cells and adhering onto coated culture dishes and culturing in the culture media for at least 1 day. In this method, EBs are generated from stem cells by the scraping methods and are cultured for at least 1 day in the culture medium. Aggregates are optionally cultured in suspension for 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or more days prior to dissociating and adhering on the coated culture dishes.

In a further embodiment, culturing the dissociated cells in b) comprises adhering the dissociated cells from a) onto coated culture dishes or feeders and culturing for at least 3 days in the culture media. The cells are optionally cultured in adherent cultures for 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or more days.

The term “osmolality” as used herein refers to the concentration of a solution in terms of osmoles of solute per kilogram of solvent. Osmoles of solute per kilogram of solvent is equivalent to the number of particles per kg. In this case, it is the concentration of ions (originating from salt: NaCl=2) per kg of solvent, which is double the molality (mol/kg), which refers to molecules/kg. A person skilled in the art would readily be able to determine the amount of salt needed to obtain media of a particular osmolality. An example of such a determination is found in Example 5.

Stem cell culture media are known in the art. In one embodiment, the culture media is serum-free. In another embodiment, the culture media comprises Dulbecco's minimal essential medium. The culture media may further comprise vitamins, trace elements, selenium, insulin, lipids, β-mercaptoethanol, non-essential amino acids, antibiotics, bFGF, B27, N2 or mixtures thereof. Examples of typical culture media include mTeSR®1-F, Knockout™ D-MEM, Neurobasal™ medium, and TeSR™2. Some of the components can also be used for the medium to differentiate stem cells, for example B27, bFGF and N2 are commonly used for ectodermal induction. Combinations of these components can also be used for meso- and endodermal induction. In one embodiment, the culture media described herein comprises pluripotency or factor free media comprising the components shown in Table 2 and the osmolality is adjusted to the desired level by addition of salt as described herein.

The term “stem cell” as used herein refers to a cell that has the ability for self-renewal. In one embodiment, the stem cell is a pluripotent stem cell. The term “pluripotent” as used herein refers to an undifferentiated cell that maintains the ability to allow differentiation into various cell types. In one embodiment, pluripotency is determined morphologically for example as described in Example 4. In such an embodiment, a cell is considered pluripotent when the colony the cell is part of displays less than 1% of differentiation. In one embodiment, the pluripotent stem cell is an embryonic stem cell. In another embodiment, the pluripotent stem cell is an induced pluripotent stem cell derived from any somatic cell using genetical or chemical methods.

Embryonic stem cells can be obtained from the inner cell mass of an early mammalian embryo—the blastocyst. Induced pluripotent stem cells (iPSCs) are obtained by re-programming somatic cells of the body. The term “pluripotent stem cells” includes, without limitation, cultured embryonic stem cell lines and induced pluripotent stem cell lines derived from any tissue. Induced pluripotent stem cells can be derived from mammalian cells. Stem cells have also been discovered in non-mammalian sources such as zebra fish, drosophila and newts. In one embodiment, the pluripotent stem cells are human.

In one embodiment, the aggregates or clusters are formed in the presence of Y27632 (rock inhibitor), which is added to increase the survival of single stem cells.

The term “aggregate” as used herein refers to one cell attached to another cell or more than one cell attached together or a group of cells attached together. Such aggregates are formed from cells after disruption of confluent or semi-confluent culture of human pluripotent stem cells or from clusters of cells obtained by disruption of confluent or semi-confluent culture of human pluripotent stem cells. The term “embryoid body” or “EB” as used herein refers to a three-dimensional aggregate derived from human pluripotent stem cells. Embryoid bodies are formed using various protocols including scraping of human pluripotent stem cells. Aggregates and embryoid bodies are used interchangeably. However in some instances aggregates will specifically refer to aggregates when using the microwell device called AggreWell™400 as shown in Example 7 or AggreWell™800 as shown in Example 24. In one embodiment, the embryoid bodies comprise 500 to 20,000 cells.

In a further embodiment, the dissociated and adhered cultures in c) are cultured in said culture medium for at least 1 day, optionally 3-6 days.

The term “dissociation” as used herein refers to the breaking up of cell aggregates or clusters into smaller aggregates or different sizes or into a single cell suspension. Dissociation of the cells described herein can be by any method, including, without limitation, enzymatic, chemical or mechanical means. In one embodiment, dissociation comprises mechanical means. In another embodiment, dissociation comprises enzymatic means, such as Accutase, Dispase, Neurocult® Chemical Dissociation Kit or trypsin.

In one embodiment, the coated culture dishes comprise factors which promote cell attachment, such as extracellular matrix molecules, synthetic molecules, synthetic peptides or chemical substrates. In another embodiment, the coated culture dishes comprise poly-L-ornithine/laminin, laminin alone or Matrigel. The concentration of laminin is readily determined by a person skilled in the art and includes, 1-20 ug/mL, such as 1 ug/mL, 5 ug/mL, 10 ug/mL or 20 ug/mL. The concentration of poly-L-ornithine is readily determined by a person skilled in the art and includes, 1-100 ug/mL, such as 1 ug/mL, 5 ug/mL, 10 ug/mL or 20 ug/mL

The term “differentiation” as used herein refers to the process by which a less specialized cell, such as a stem cell, becomes a more specialized cell type, such that it is committed to a specific lineage including, without limitation, certain progenitor cells as well as more specialized somatic cells. Conditions for differentiation of the stem cells are readily known in the art.

The term “germ layer progenitor cells” as used herein refers to cells that are able to differentiate into the three layers of cells that are formed during mammalian embryogenesis. Accordingly, in one embodiment, the germ layer is ectodermal, which refers to the outer germ layer that develops into skin and nervous tissue; endodermal, which refers to the inner germ layer that develops into the lining of the digestive and respiratory systems; and/or mesodermal, which refers to the middle germ layer that develops into muscle, bone and cartilage and blood and connective tissue.

Ectodermal Differentiation

The present inventors have shown that an ectodermal germ layer can be induced by culturing the stem cells in a culture media with an osmolality range of 260 to 280 mOsm/kg for dissociated cells that are first cultured in the microwell device and/or in suspension and with an osmolality range of 270 to 320 mOsm/kg for dissociated cells directly plated onto coated culture dishes according to the methods described herein. Accordingly, in one embodiment, the osmolality of the culture medium is 260 to 280 mOsm/kg for inducing ectodermal progenitor cells. In another embodiment, the osmolality of the culture media used in the methods described herein is 270 to 320 mOsm/kg for inducing ectodermal progenitor cells.

In yet a further embodiment, the methods described herein further comprise identifying ectodermal or neural progenitor cells based on the presence of markers associated with neural cell fate selected from Pax6, Sox1, Sox2, A2B5, CD15, CD24, CD29, CD81, CD133, PSA-NCAM, Vimentin, Musashi1, Musashi2 and Nestin.

The present disclosure also provides a method of maintaining single neural progenitor cells in culture media with an osmolaltiy of 260-340 mOsm/kg comprising generating ectodermal progenitor cells according to the methods described herein, dissociating the ectodermal progenitor cells from the adhered cultures; plating and culturing said progenitor cells for at least 1 day. In one embodiment, the single neural progenitor cells are maintained in the presence of bFGF. In another embodiment, the progenitor cells are plated and cultured for at least 4 days. In one embodiment, the cells are plated on coated culture dishes. In an embodiment, the coated culture dishes comprise factors which promote cell attachment, such as extracellular matrix molecules, synthetic molecules, synthetic peptides or chemical substrates. In another embodiment, the coated culture dishes comprise poly-L-ornithine/laminin. Typical concentrations of laminin are as described herein.

In one embodiment, the bFGF is at a concentration of 10-100 ng/mL. In another embodiment, the cells are propagated and maintained in culture for at least 3 passages. In one embodiment, the cells are propagated and maintained on coated culture dishes as described herein.

The present inventors found that incubation of adhered cultures with a buffer of Ca²⁺ and Mg²⁺ free 1×PBS buffer with a pH of 7.0 to 8.0 allowed selective release or dissociation of single neural progenitor cells. Accordingly, in another embodiment, the single neural progenitor cells are dissociated in a buffer comprising a Ca²⁺ and Mg²⁺ free 1×PBS or 1× Hank's Buffered Solution with a pH of 7.0 to 8.0. In one embodiment, the single cells are incubated in the buffer for 1 to 2 hours. In another embodiment, the cells are incubated in the buffer for 30-90 minutes.

In yet another embodiment, the cells are cultured in neuronal cell differentiation medium comprising DMEM-F12, N2, B27 or combinations thereof, non-essential amino acids, hormones, lipids, BDNF, GDNF, ascorbic acid, retinoic acid, TGF-β (neurons), sonic hedgehog (SHH), thyroid hormone, any member of the BMP family, EGF and PDGF (oligodendrocytes), cyclopamine or any other SHH inhibitor (astrocytes) to produce differentiated cells. The differentiated cells are optionally propagated and maintained on a coated culture dish as described herein. For differentiation, bFGF is removed. In one embodiment, the differentiated cells comprise neurons, astrocytes or oligodendrocytes, which are optionally identified based on the presence of markers selected from TUJ1, MAP2 (neurons), A2B5, GFAP, GLAST (glial cells, astrocytes and radial glial cells), FGFR1, FGFR2, FGFR3, FGFR4, O4, OLIG2, GalC, and NG2 (oligodendrocytes).

Endodermal/Mesodermal Differentiation

The present inventors have shown that an endodermal/mesodermal germ layer can be induced by culturing stem cells in a culture media with an osmolality range higher than 280 mOsm/kg, optionally 290-340 mOsm/kg for dissociated cells cultured in the microwell device and/or in cell suspension prior to plating on coated culture dishes by the methods described herein and an osmolality above 320 mOsm/kg, optionally 320 to 340 mOsm/kg, for dissociated cells plated directly onto coated culture dishes by the methods described herein. Accordingly, in another embodiment, the osmolality of the culture media used in the methods described herein is higher than 280 mOsm/kg for inducing endodermal/mesodermal progenitor cells. In another embodiment, the osmolality of the culture medium is 290, to 340 mOsm/kg, for inducing endodermal/mesodermal progenitor cells. In yet another embodiment, the osmolality of the culture media used in the methods described herein is higher than 320 mOsm/kg for inducing endodermal/mesodermal progenitor cells. In yet a further embodiment, the osmolality of the culture medium is 320 to 340 mOsm/kg for inducing endodermal/mesodermal progenitor cells.

In one embodiment, a culture medium at an osmolality higher than 280 mOsm/kg, optionally higher than 320 mOsm/kg, provides differentiation into mesodermal fate, which can give rise to mesenchymal stem cells, chondrocytes, cardiomyocytes, hematopoietic stem cells and skeletal cells. In another embodiment, a culture medium at an osmolality higher than 280 mOsm/kg, optionally higher than 320 mOsm/kg, provides differentiation into endodermal fate, which can give rise to pancreas, intestinal cells and liver cells.

In yet a further embodiment, the methods described herein further comprise identifying endodermal and/or mesodermal progenitor cells based on the presence of markers selected from Sox17, HNF1β, HNF3β, Gata4, Gata6, CXCR4 (CD184), AFP (endoderm) and Bry, MixL1, Snail, Bmp2, Bmp4, CD31, and CD34 (mesoderm).

The present disclosure also provides a method of maintaining single endodermal or mesodermal progenitor cells in culture media with an osmolality of 290 to 340 mOsm/kg comprising generating endodermal or mesodermal progenitor cells according to the methods described herein, dissociating single endodermal or mesodermal progenitor cells from the adhered cultures; and plating and culturing said progenitor cells. In one embodiment, the cells are plated on coated culture dishes as described herein.

In one embodiment, inductive factors are added to the culture media to obtain endoderm and mesoderm. The factors, for example, comprise members of the BMP and FGF family as well as activin A (Boyd et al., 2009; Kubo et al., 2004; Lee et al., 2009, Takei et al., 2009, Sulzbacher et al., 2009).

In one embodiment, the cells are propagated and maintained in culture for at least 3 passages. In one embodiment, the cells are propagated and maintained on coated culture dishes as described herein.

The present inventors found that incubation of adhered cultures with a buffer of Ca²⁺ and Mg²⁺ free 1×PBS buffer with a pH of 7.0 to 8.0 allowed release or dissociation of single ectodermal or neural progenitor cells. Accordingly, in another embodiment, the endodermal or mesodermal progenitor cells are obtained by releasing ectodermal cells from the culture by dissociating in a buffer of Ca²⁺ and Mg²⁺ free 1×PBS buffer with a pH of 7.0 to 8.0, thus leaving the endodermal and/or mesodermal cells adhered to the plate for culturing. The endodermal and mesodermal progenitor cells do not detach from the surface and therefore this method is removing the ectodermal progenitor cells, leaving an enriched population of endodermal and mesodermal cells, which can then be dissociated.

In yet another embodiment, the cells are cultured in mesodermal or endodermal cell differentiation medium to produce differentiated cells. Said differentiated cells are optionally propagated and maintained on coated culture dishes as described herein. Such differentiation medium includes, without limitation, fetal bovine serum (FBS), members of the BMP and FGF family, follistatin, Noggin, and activin A. In one embodiment, the differentiated cells comprise mesenchymal stem cells, chondrocytes, cardiomyocytes, hematopoietic stem cells, skeletal muscle cells (mesoderm), pancreatic cells, intestinal cells or liver cells (endoderm).

In another embodiment the differentiated cell lineages are identified using the differentiation markers, including, without limitation, Stro1, Collagen2, MyoD, Sox9, Actin, Msx2, Runx2, DIx5 (mesenchymal stem cells); CD44, CD151, Sox9, Osteonectin, Collagen 2 (chondrocytes), MyoD (cardiomyocytes), CD34, CD31, CD133, Tie2 (hematopoietic stem cells), Actin, α-actinin, MyoD, Desmin (skeletal muscle cells), Islett Islet2, Pdx1, Insulin (pancreatic cells), Hnf1β, Cdx2 (intestinal cells), Albumin, ApoE (liver cells).

ASSAYS OF THE DISCLOSURE

The cells generated by the methods described herein will allow experimental dissection of the events during early development of the nervous system, and the identification of new genes and polypeptide factors which may have a therapeutic potential such as for induction of regenerative processes. Additional pharmaceutical applications may include the development of toxicity assays and drug discovery platforms, such as high-throughput screens for neuroprotective compounds. Generation of neural progenitors from hES cells in vitro may serve as an unlimited source of cells for potential cell therapies for neurodegenerative diseases and for the delivery and expression of factors in the nervous system.

The neural progenitor cells and differentiated neural cells that are generated by the methods described herein may be used for the study of the cellular and molecular biology of human neural development, for the discovery of genes, growth factors, and differentiation factors that play a role in neural differentiation and regeneration, for drug discovery and for the development of screening assays for teratogenic, toxic and neuroprotective effects.

Accordingly, the present disclosure provides a method of screening germ layer cells comprising

-   -   (a) preparing a culture of ectodermal, endodermal and/or         mesodermal germ layer cells by the methods described herein;     -   (b) treating the germ layer cells with a test agent or agents;         and     -   (c) subjecting the treated germ layer cells to analysis.

In another embodiment, there is provided a method of screening neural progenitor cells comprising

-   -   (a) preparing a culture of neural progenitor cells by the         methods described herein;     -   (b) treating the neural progenitor cells with a test agent or         agents; and     -   (c) subjecting the treated neural progenitor cells to analysis.

In one embodiment, the test agent is a chemical or other substance being tested for its effect on differentiation of the germ layer cells or neural progenitor cells into specific cell types. In such an embodiment, the analysis may comprise detecting markers of differentiated cell types. For neural differentiation from ectodermal or neural progenitor cells, markers include, without limitation, Nestin, Sox1, and TUJ1. For endodermal differentiation from endodermal cells, the markers include, without limitation, Sox7, Sox17, HNF1β, HNF3β, Gata4, Gata6, CXCR4 (CD184), alpha-fetoprotein (AFP) (endoderm). For mesodermal differentiation from mesodermal cells the markers include, without limitation Bry, MixL1, Snail, Bmp2, Bmp4, CD31, CD34, (mesoderm). In an embodiment, the screening assay is used to identify compounds that may have therapeutic potential such as for induction of regenerative processes or providing neuroprotective compounds.

In another embodiment, the test agent is a chemical or drug and the screening is used as a primary screen or as a secondary pharmacology and toxicology evaluation screen for the chemical or drug.

CULTURE MEDIA OF THE DISCLOSURE

The present disclosure also provides culture media compositions useful for inducing germ layer progenitor cells. In one embodiment, the culture media comprises an osmolality lower than 340 mOsm/kg. In another embodiment, the culture media comprises an osmolality of 240 to 340 mOsm/kg. In yet another embodiment, the culture media comprises an osmolality of 260 to 340 mOsm/kg.

The present disclosure also provides culture media compositions for use in inducing ectodermal germ layer progenitor cells. In one embodiment, the culture media comprises an osmolality of 260 to 280 mOsm/kg. In another embodiment, the culture media comprises an osmolality of 270 to 320 mOsm/kg. The present disclosure further provides culture media for use in inducing mesodermal and/or endodermal germ layer progenitor cells. In one embodiment, the culture media comprises an osmolality above 280 mOsm/kg, optionally, 290 to 340 mOsm/kg. In another embodiment, the culture media comprises an osmolality above 320 mOsm/kg, optionally, 320 to 340 mOsm/kg.

The culture media can be any culture media useful in differentiating stem cells. For example, the culture media is optionally pluripotent factor free or factor free media comprising the components shown in Table 2 and adjusted for the desired osmolality, optionally 260-340, 260-280, 290-340 or about 270 mOsm/kg. A person skilled in the art would readily understand how to adjust the osmolality of the solution, for example, the osmolality can be adjusted by adding salt as described in Example 5. Briefly, the amount of salt to be added to a 5× supplement is calculated using the following formula: For example to obtain an osmolality of 270 after mixing a 5× supplement (initial osmolality of 100 mOsm/kg) and a basal medium (here: initial osmolality of 300 mOsm/kg): [270−((0.8×300 mOsm)+(0.2×100 mOsm))]/2000×58.44×1.05=0.30 g/L of NaCl

The osmolality of 270 can be achieved by any other media preparation methods and starting medium formulation by adjusting the concentration of NaCl.

The above disclosure generally describes the present disclosure. A more complete understanding can be obtained by reference to the following specific examples. These examples are described solely for the purpose of illustration and are not intended to limit the scope of the disclosure. Changes in form and substitution of equivalents are contemplated as circumstances might suggest or render expedient. Although specific terms have been employed herein, such terms are intended in a descriptive sense and not for purposes of limitation.

The following non-limiting examples are illustrative of the present disclosure:

EXAMPLES Example 1 Culture of Human Pluripotent Stem Cells as Aggregates in Defined Serum-Free Medium on BD Matrigel™ Coating

Human pluripotent cells were maintained on BD Matrigel™ coated dishes in defined serum-free medium. A detailed protocol can be found in manual #29106 “Maintenance of Human Embryonic Stem Cells in mTeSR®1” by STEMCELL TECHNOLOGIES INC. for the maintenance of human pluripotent stem cells which includes the procedure for BD Matrigel™ coating. Cells were passaged when the colonies were large, beginning to merge, and had centers that are dense and phase-bright compared to their edges (see FIG. 1). Depending on the size and density of seeded aggregates, cultures were passaged 5-7 days after initial seeding.

Medium was aspirated from the stem cell culture and cells were rinsed with DMEM/F-12 (2 mL/well). 1 mL of dispase (STEMCELL TECHNOLOGIES INC. catalogue #07923) was added per well at a concentration of 1 mg/mL. The dish was placed at 37° C. for 7 minutes.

Once the colony edges appeared slightly folded back, dispase was removed, and each well was gently rinsed 2-3 times with 2 mL of DMEM/F-12 per well to dilute away any remaining dispase. 2 mL/well of DMEM/F-12 or mTeSR®1 was added to the well and colonies were scraped off with a cell scraper (e.g. Corning Catalog #3010) or a serological pipette tip.

The detached cell aggregates were transferred to a 15 mL conical tube and the well was rinsed with an additional 2 mL of DMEM/F-12 to collect any remaining aggregates. The rinsed media containing remaining cells was added to the same 15 mL tube.

The 15 mL tube containing the aggregates was centrifuged at 300×g for 5 minutes at room temperature (15-25° C.). The supernatant was aspirated. For each well of hESC aggregates collected in the 15 mL tube, 1-2 mL of mTeS®1 were added. The pellet was resuspended gently by pipetting up and down using a P1000 micropipette (1-2 times). Cells were maintained as aggregates. Using the “clump count” method the number of clumps was estimated. To enumerate clumps that are likely to attach and grow of the right size (˜50-60 μm in diameter), a micrometer placed in the microscope eyepiece is used. To perform the clump count, 30 μL of DMEM/F-12 were aliquoted into 2 wells of a 96-well flat-bottom plate. A “+” was drawn centered on the bottom of these wells to serve as a counting grid. 5 μL of a freshly mixed clump suspension was added to each well. Clumps were counted in duplicate that were approximately 3500 μm² or greater. This corresponds to clumps with a diameter of approximately 60 μm. The total number of clumps per μl was estimated using the formula: Total # of clumps perμl=xclumps counted/5 μL total volume of suspension

A defined number of clumps according to the size of the well or dish that is being seeded was plated. The volume of clump suspension (y) used to seed new dishes was calculated using the guide in Table 1 for appropriate seeding densities. For example (y) for a 6-well equals: 350/# clumps counted per μl.

hESC aggregates were plated with 2 mL of mTeSR®1 per new 6-well coated with BD Matrigel™. The plate was moved in several quick, short, back-and-forth and side-to-side motions to disperse cells evenly across the surface of the wells. The plate was placed in a 37° C. incubator. hESCs cultured in mTeSR®1 and BD Matrigel™ can be used as a consistent source of cells for the differentiation protocols in this disclosure. FIG. 1 shows undifferentiated H9 hESCs at passage 51 on day 5 of culture.

Example 2 Preparation of Mouse Embryonic Fibroblast Layers (Mefs) for maintenance cultures of hES cells

Irradiated embryonic day 13 mouse embryonic fibroblasts (MEF's) (CF-1 mouse strain) were prepared according to standard protocols (WiCell Research Institute web page: https://www.wicell.org and Dravid et al., Human Embryonic Stem Cell Protocols, Humana press). The day prior to plating human pluripotent stem cells onto the MEFs, a vial of irradiated MEFs was thawed into standard “MEF-medium” according to the WiCell Research Institute's standard protocols. Approximately 2×10⁴ cells/cm², which corresponds to approximately 2×10⁵ cells per 6-well, were plated. FIG. 2 shows hESCs cultured on MEFs at day 4.

Example 3 Culture of Human Pluripotent Stem Cells on Mouse Feeder Cells

Human pluripotent stem cells maintained on mouse feeder cells can also be used as a consistent source of cells for the differentiation protocols in this disclosure.

H9 hESCs were grown on MEF's (see Example 2) in hESC medium (DMEM-F12 (STEMCELL TECHNOLOGIES INC., catalog #36254), 25% knock-out serum replacer (Invitrogen, catalog #10828028), 200 mM L-glutamine (Invitrogen, catalog #25030081), 0.1 mM β-mercaptoethanol (Sigma, catalog #63689), 1×NEAA solution (Invitrogen, catalog #11140050), 4 ng/ml bFGF (STEMCELL TECHNOLOGIES INC., catalog #02634) according to the WiCell Research Institute's standard protocols which can be found on the WiCell Research Institute web page (https://www.wicell.org) and Dravid et al., Human Embryonic Stem Cell Protocols, Humana press).

Briefly, cells were split when the feeder layer was more than 2 weeks old; colonies started to merge or became large with dense centers. For passaging of human pluripotent stem cells, a 1 mg/ml collagenase type IV (STEMCELL TECHNOLOGIES INC., catalog #07909) solution in DMEM/-F12 was used per 6-well. The culture medium was aspirated and collagenase solution was added for 5 minutes at 37° C. Using a 5-ml serological pipette, cells were scraped off the plate, while slowly pipetting the collagenase solution up and down to wash the cells of the surface. The suspension was transferred into 15-ml conical tube (Falcon) and was centrifuged at 300 g for 5 minutes. The supernatant was aspirated and 2-3 ml of hESC medium was added. By gently tapping the tube, the pellet was reconstituted and centrifuged again at 300×g for 5 minutes. In the meantime, media was aspirated from the MEF's and cells were washed 2× with 1×PBS (Ca, Mg free), pH 7.4. Supernatant was removed from the pelleted hESCs and 12 ml of fresh hESC medium were added. Using a 10-ml serological pipette, the pellet was carefully resuspended and the cell suspension was distributed onto the 6-well plate of MEFs (this equals a 1:6 split ratio of the hESCs). The plate was moved back-and-forth and side-to-side several times to distribute the cells evenly. The plate was then returned to the incubator.

Example 4 Morphological Assessment of Pluripotency of Human Pluripotent Stem Cells (hPSCs) Grown in mTeSR®1 on BD Matrigel™

For the successful induction of germ layers, a highly pure population of pluripotent stem cells was used. The following criteria were employed to assess the morphology and quality of cells (described in technical manual #29106 by STEMCELL TECHNOLOGIES INC.): Undifferentiated human pluripotent stem cells, grew as compact, multi-cellular colonies, as shown in FIG. 1. They exhibited a high nuclear-to-cytoplasm ratio and prominent nucleoli. These colonies were characterized by a distinct border. Healthy hPSCs colonies were multilayered in the center, resulting in clusters of phase-bright cells when viewed under phase contrast. Differentiation was characterized by loss of border integrity, gross non-uniform cell morphology within the colony and the emergence of obvious alternate cell types. The percentage of pluripotency was estimated by observation of the colonies under the microscope (using 4× and 10× objectives). Cells were used for germ layer induction only when they displayed less than 1% of differentiation. FIG. 3 shows pluripotent stem cells in the left column and an example of a colony with a differentiating center (red box and close-up) in the right column.

Example 5 Media Formulations with Different Osmolality Ranges Factor Free mTeSR®1 Medium with Modified Osmolalities

The complete media formulation and method of preparation for modified TeSR (mTeSR®1, STEMCELL TECHNOLOGIES INC., catalogue #05850) is published in Ludwig et al, Nature Methods 3(8): 637, 2006. It is based on the original TeSR formulation published in Ludwig et al., Nature Biotechnology 24(2): 185, 2006, with the following modification: substitution of human serum albumin (HSA) with bovine serum albumin (BSA).

To manufacture the factor free mTeSR®1 (mTeSR®1-F) media, a 5× supplement was produced containing all of the mTeSR®1 reagents at 5-fold concentrations, with the exceptions of the following 5 factors: GABA, pipecolic acid, bFGF, TGFβ1, lithium chloride. The components for the media are shown in Table 2.

After mixing the components of the 5× supplement together, the pH was adjusted to 7.4 by adding 10N NaOH. The osmolality of the solution was measured using a standard osmometer. The initial osmolality of the 5× supplement was usually around 100 mOsm/kg, and salt (NaCl) was used to increase the osmolality while taking into account that the 5× supplement is combined with 400 mL of the base medium DMEM/F12 (Hyclone, catalog #SH30004) (with an osmolality of around 300 mOsm/kg) to obtain mTeSR®1-F. The amount of salt that had to be added to the 5× supplement was calculated using the following formula: For example to obtain an osmolality of 270 after mixing the 5× supplement and the basal medium: [270−((0.8×300 mOsm)+(0.2×100 mOsm))]/2000×58.44×1.05=0.30 g/L of NaCl

The x amount of NaCl was added to the 5× supplement. Four media with different osmolalities were prepared: 260 mOsm/kg, 280 mOsm/kg, 320 mOsm/kg and 340 mOsm/kg.

Example 6 Generating a Single Cell Suspension of Human Pluripotent Cells for EB Formation in AggreWell™400

The procedure to generate single cells from human pluripotent stem cell colonies and use them in the AggreWell™400 protocol and device is described in technical manual 29146 (STEMCELL TECHNOLOGIES INC.). Briefly, 10-cm plates containing undifferentiated H1 passage 46 hESCs at semi-confluence were removed from the incubator and placed inside a sterile tissue culture hood. mTeSR®1 maintenance medium was aspirated from the H9 cultures, and each plate was then rinsed with 2 mL of 1×PBS (Ca, Mg free), pH 7.4 was then aspirated and discarded. Accutase (STEMCELL TECHNOLOGIES INC. catalogue #07920) was used to dissociate the adherent hESC culture into single cells. 3 mLs of Accutase were added directly to each 10-cm plate containing undifferentiated H9 cell cultures. Plates were then incubated at 37° C. for approximately 10 minutes, or until cells detached easily from the plate with gentle shaking. The H1 cell suspension was gently pipetted 2-3 times with a serological pipette to ensure any remaining clumps were fully dissociated and to dislodge any cells that were still attached to the surface of the dish. The suspension was transferred to a 50 mL conical tube. Each plate was rinsed with 10 mL of 1×PBS (Ca, Mg free), pH 7.4 and the rinsing solution was transferred to the same 50 mL tube containing the cell suspension.

H9 hESCs grown on MEFs (see Example 3) were dissociated into a single cell suspension using the same procedure. Most feeder cells within the EBs died during EB formation and are believed to not disturb the germ layer induction process within the EBs.

Cell suspensions were centrifuged at 350×g for 7 minutes at room temperature (15-25° C.). The supernatant was aspirated and discarded. Cell pellets were resuspended in a 1 mL volume of the medium mTeSR®1-F of osmolality 270, 290, 320 or 340 mOsm/kg. Y27632 rock inhibitor (STEMCELL TECHNOLOGIES INC. catalogue #07171/2) was also added to the medium at a final concentration of 10 μg/mL to enhance cell survival during EB formation (Watanabe et al, 2007). Viable cells were counted using standard techniques, by diluting a 10 μL sample of the cell suspension 1:10 in 90 μL of trypan blue (Invitrogen, catalog #15250061) and counting unstained cells on a haemocytometer. The number of cells per μl allows calculating the volume of cells to use for EB formation (Example 7). One 10-cm dish of hESCs gave rise to 7-10×10⁶ cells.

Example 7 EB Formation from Human Pluripotent Stem Cells Using a Microwell Device (AggreWell™400) in mTeSR®1-F 270, 290, 320 and 340 mOsm/kg Media to Induce the 3 Germ Layers

Controlled sized EBs can be generated very efficiently using AggreWell™400. Briefly, undifferentiated H1 hESCs were cultured to semi-confluency, using the method of Example 1. As described in technical manual #29146 (STEMCELL TECHNOLOGIES INC.), an AggreWell™400 plate was removed from the packaging in a sterile tissue culture hood. Each of the 8 microwell-containing wells of the plate was rinsed with 1 mL of 1×PBS (Ca, Mg free), pH 7.4, and the PBS was then removed by aspiration. 1 mL of medium was added to each well of the AggreWell™400 plate. To induce the three different germ layer cell types: ectoderm, endoderm and mesoderm, media with 4 different osmolalities were used for EB formation: 270 mOsm/kg, 290 mOsm/kg, 320 mOsm/kg and 340 mOsm/kg (preparation: see Example 4). Y27632 rock inhibitor was also added to the medium at a final concentration of 10 μg/mL to enhance cell survival during EB formation. The AggreWell™400 plate was centrifuged at 3000×g for 2 minutes in a swinging bucket rotor fitted with a plate holder to remove any small bubbles from the microwells. AggreWell™400 plates were then set aside while preparing a single cell suspension of H1 hESCs cells using the method of Example 6. A volume of the cell suspension containing 2.4×10⁶ cells was added to each well of the AggreWell™400 plate prepared previously. This amount of cells will distribute into the approximately 1200 microwells to form EBs of approximately 2,000 cells each. Medium was added as above, to a final volume of 2 mL per well. The AggreWell™400 plate was centrifuged at 100×g for 3 minutes to capture the cells in the microwells. Plates were incubated at 37° C. with 5% CO₂ and 95% humidity for 24 hours. FIG. 4 shows the distributed single H1 hESCs cells within the microwells of an AggreWell™400 well.

Example 8 EB Formation by the “Scraped EB” Method and Culture in Suspension Cultures to Induce Differentiation into the Three Germ Layers

EBs can also be routinely generated by the scraping method which does not allow control for size and shape of EB. To form EBs, adherent human pluripotent stem cell colonies were lifted from the tissue culture plate using mechanical scraping. The resulting randomly sized clumps of cells were placed into non-adherent suspension culture and EBs were incubated in a standard tissue culture incubator, at 37° C., 5% CO₂ and 95% humidity for a period of 5 days, with a media change every 2 days. For this purpose, the dish was tilted towards one side and using a 1000-μl pipette tip, approximately half the volume of the medium was removed without disturbing the EBs. For induction of the 3 germ layers the same media were used as described in Example 7. Fresh medium was added up to 5 ml. EBs were further processed for ectoderm, mesoderm and endoderm induction as described in Example 9 and 11-13. FIG. 5 shows scraped EBs 1 day after formation in mTeSR®1-F 270 mOsm/kg.

Example 9 Five Day Suspension Culture of EBs in Mtesr®1-F 260, 270 and 280 mOsm/kg to Induce Neuroectodermal Cell Lineages

EBs were formed from H9 hESCs cells as described in Example 7. Briefly, a single cell suspension containing 2.4×10⁶ human ES cells was added to a well of AggreWell™400, to generate approximately 1200 EBs of 2,000 cells each.

EBs were then harvested in a sterile tissue culture hood, by gently pipetting up and down the medium in the AggreWell™400 microwells 2-3 times with 1 mL disposable pipette tip to dislodge most of the EBs. To harvest the EBs, the suspension was passed through an inverted 40 μm nylon cell strainer (Falcon) sitting on top of a 50 mL conical tube to remove unaggregated single cells and debris. AggreWell™400 surface was washed a further 5 times with 1 mL each of DMEM/F-12, pipetting across the entire surface to dislodge all aggregates. All washes were applied onto the cell strainer membrane. The cell strainer was turned upside down, holding it close over a low-adherence 6-well. EBs were washed of the membrane using mTeSR®1-F 260, 270 or 280 mOsm/kg medium to induce differentiation of the formed EBs into neuroectoderm. Approximately 5 ml of medium were used to remove the EBs from the nylon membrane holding the strainer over a single well of a 6-well ultra-low adherence dish (STEMCELL TECHNOLOGIES INC., catalog #27145). EBs were incubated in a standard tissue culture incubator, at 37° C., 5% CO₂ and 95% humidity for a period of 5 days, with a media change every 2 days. For this purpose, the dish was tilted towards one side and using a 1000-μl pipette tip, approximately half the volume of the medium was removed without disturbing the EBs. Fresh medium was added up to 5 ml. FIG. 6 shows the released EBs after 24 hours of incubation in the AggreWell™400 plate at 2×, 10× and 40× magnification. There were no morphological differences observed at the time of recovery of EBs from the AggreWell™400 plates.

Example 10 Induction of In Vitro Differentiation of Human Pluripotent Stem Cells into Neural Progenitors in Adherent Monolayer Culture Containing Media in an Osmolality Range of 270 to 320 mOsm/kg

For this purpose human pluripotent stem cells were used either as clusters or as single cell layers plated on BD Matrigel™ or onto human or mouse feeder cells. To plate cells as clusters 1×PBS (Ca, Mg free), pH 7.4 was used to dissociate stem cell colonies. Alternatively, any enzymatic, chemical or mechanical method that generated clusters of hESC can be used, such as but not limited to collagenase, dispase or mechanical scraping. Cells were rinsed with 1×PBS (Ca, Mg free), pH 7.4 after removal of culture media. The PBS was left on the cells for approximately 10 minutes at room temperature. Cells were gently pipetted up and down using a 5-mL serological pipette and transferred into a 15 mL conical tube. Clumps were centrifuged at room temperature at 350×g for 5 minutes. The 1×PBS (Ca, Mg free), pH 7.4 was removed and cells were resuspended in 1 mL of either mTeSR®1-F 270 or 320 mOsm/kg, briefly shooting them off the bottom of the tube using a 1000 μl pipette tip. Optionally, N2A (STEMCELL TECHNOLOGIES INC., catalog #07152) and B27 (STEMCELL TECHNOLOGIES INC., catalog #07153) at a 1× concentration were added to the induction media. The cell clump suspension was distributed between 5 wells of a 6-well plate coated with BD Matrigel™.

To obtain single cell suspensions to use for adherent induction, the method of Example 6 was used. Cells were plated at densities of approximately 2×10⁵ cells per 6-well into mTeSR®1-F 270 or 320 mOsm/kg. Medium was changed every 2 days.

FIG. 7 shows neural progenitor cells emerging from the seeded clumps after 5 days of induction. During neural differentiation human pluripotent stem cells undergo morphogenetic events characterized by the formation of radially organized columnar epithelial cells termed “neural rosettes” (Zhang et al. 2001; Perrier et al. 2004). These structures comprise cells that are capable of differentiating into various region-specific neuronal and glial cell types in response to appropriate developmental cues (Perrier et al. 2004; Li et al. 2005). Rosettes appear in different sizes and shapes and can be easily identified. In both media (mTeSR®1-F 270 and 320 mOsm/kg) rosettes formed with almost the same efficiencies and were visible after 3 days. The induction period was 5-6 days. Arrows point towards some examples of rosettes.

Example 11 Plating of EBs after Suspension Cultures in mTeSR®1-F 260, 270 and 280 mOsm/kg to Enable Outgrowth of Neuroectodermal Progenitors

After EB formation and cultivation using the methods of Examples 6 and 7, the EBs were visualized under the microscope. There was no obvious morphological difference observed in the EBs cultivated in different osmolalities.

To be able to cultivate individual neural progenitor cells, using optionally mechanical trituration the EBs were dissociated into small clusters. Alternatively, other chemical methods alone or in combination with enzymatic dissociation methods, or enzymatic dissociation may be used for this purpose. This procedure enabled the neural progenitor cells to grow out from these structures and form multi-layered clusters of cells and single cell layers. For mechanical trituration, EBs were transferred from 6-well plates into conical 15 mL tubes using a 1000 μl-pipette tip. EBs were left to settle to the bottom of tube, by incubating for 5 mins at room temp. Supernatant was removed, leaving pelleted EBs at the bottom of the tube. 1 ml of fresh mTeSR®1-F 260, 270 or 280 mOsm/kg was added to corresponding tubes. Using a 1000 μl-pipette tip, cells were dissociated by pipetting up and down 5-20 times depending on the consistency of the EBs until a cell suspension containing barely visible small clusters was generated. The cell suspension of one 15 mL tube (corresponding to EBs that were cultured in one 6-well) was distributed onto 3 wells of a 6-well dish each containing 3 glass coverslips coated with Poly-L-Ornithine/Laminin (see Example 18). Media was filled up to 2 ml and cells were distributed evenly by gently rocking the plate back and forth. The dishes were placed back into 37° C. Attachment was observed after several hours. FIG. 8 shows the attached EBs after 2 days. Arrows point towards some examples of rosettes. Rosettes are present in all 3 media and can be seen after 2 days of attachment. The percentage of rosettes and therefore the efficiency of neural induction were assessed as described in Example 12.

Example 12 Morphological Assessment of Attached EBs from Suspension Culture in Media within the Osmolality Range of 260-280 mOsm/kg to Determine the Percentage of Neuroectoderm Present

Two days after plating the dissociated EBs (see Example 11), rosette structures became apparent (FIG. 8). These neural rosettes represented a mixture of size-ranged rosettes, “ridge-like” rosettes with multiple cell layers and single cell layered “star-shaped” rosettes. Scoring criteria were set up to estimate the percentage of rosette containing colonies. To make the criteria stringent, only colonies with more than 50% of rosettes present were counted. Colonies with a lower percentage were not included. The following formula was used to calculate the total percentage of neural rosettes: “Total number of colonies/number of colonies with more than 50% of rosettes present”. FIG. 9 summarizes the results of rosette-counts.

Example 13 Five Day Suspension Culture and Plating of EBs in mTeSR®1-F with an Osmolality Range of 290 to 340 mOsm/kg to Induce Endodermal and Mesodermal Cell Lineages and Less Efficiently Ectodermal Cell Lineages

Using the methods described in Examples 6 and 7 and media mTeSR®1-F 270, 290, 320 and 340 mOsm/kg, H1 hESC were used to form EBs and induce cells of the different germ layers. EBs were cultured and adhered as described by the methods in Example 11. In comparison to mTeSR®1-F 260-280 mOsm/kg used in the previous example, clearly morphological differences are observed with osmolalities higher than 280. At an osmolality of 290 mOsm/kg, fewer rosettes were observed as compared to the lower osmolalities. The cell morphologies that can be observed after attaching the EBs are shown in FIG. 10. FIG. 17 shows an immunocytochemical staining (see Example 17) for Nestin and Sox1 on cells induced in mTeSR®1-F 270 mOsm/kg and mTeSR®1-F 340 mOsm/kg. Whereas many rosettes were observed using media with the osmolality of 270 mOsm/kg, the other 3 osmolalities showed a decrease in rosette formation. Furthermore, Nestin and Sox1 expression did not overlap in medium mTeSR®1-F 340 mOsm/kg to the same extent as in medium mTeSR®1-F 270 mOsm/kg. Most likely the other cell lineages present in the attached EB colonies were of endodermal and mesodermal origin as evident by their flat and “cobblestone-like” cells as well as flat cells and cells with a spindle-like morphologies, as published before (Odorico et al., 2001; Ferreira et al., 2007, Gerrard et al., 2005) (see FIG. 10). It is possible that these mesodermal and endodermal progenitor cells express Nestin, a phenomenon that has been described before (Wiese et al., 2004). As shown in FIG. 11, these cells look flat compared to the Nestin/Sox1 double-positive cells.

Using the scoring criteria described in Example 12, the percentages of rosettes structures and therefore of ectoderm/neural progenitor cells was estimated and the percentages of experiments performed with mTeSR®1-F 320 and 340 mOsm/kg are shown in FIG. 12.

Example 14 Selective Detachment of Neural Rosette Colonies and Plating of Neural Progenitor Cells from Adherent EB-Cultures in mTeSR®1 260-280 mOsm/kg but not in mTeSR®1 340 mOsm/kg

After a minimum of 3 days of culture in adherent conditions, with a cultivation time of 5-6 days, the colonies generated by mechanical trituration of EBs as described in Example 12, were chemically dissociated using optionally 1×PBS (Ca, Mg free), pH 7.4. An alternative chemical method may be used as well as a chemical method combined with the use of an enzyme. Also, the enzyme may be used alone or in combination with a mechanical method. Optionally, the enzyme is Accutase™.

The purpose was to obtain a single neural progenitor cell population that could be further propagated. This method was found to selectively allow for collection of neural progenitor cells. This is a novel attribute of 1×PBS (Ca, Mg free), pH 7.4 and has not been described before. Other cell types do not lift off the plate as efficiently and are not collected in the subsequent trituration step. FIG. 13 demonstrates the time-course of morphological changes/lifting off of the neural progenitor cells from the plate.

The procedure includes a brief wash with 1×PBS (Ca, Mg free), pH 7.4 after aspirating the cell culture medium. Colonies were covered with 1 ml of 1×PBS (Ca, Mg free), pH 7.4 per single well of a 6-well dish. The dishes were incubated inside a sterile cell culture hood at room temperature for a minimum of 30 minutes, optionally 90 minutes up to a maximum of 2 hours. Colonies containing neural progenitor cells started peeling off of the plate after 60 minutes (see FIG. 13). The optimal time-point for harvesting the cells was determined by trying to triturate the cells gently (usually 90 minutes). If the cells didn't lift off the plate using mild trituration, the cells were further incubated with 1×PBS (Ca, Mg free), pH 7.4. Once the cells lifted off easily, they were further triturated (optionally 5-10×), which produced a nearly single cell suspension. Cells displaying a flat morphology and not being of neural fate, stayed attached to the plate. The cell suspension was transferred to a conical 15 mL tube and centrifuged at 300×g for 5 minutes. After resuspending the cells in 1 ml of mTeSR®1-F 270 mOsm/kg containing bFGF (10 ng/mL), the cells of a single 6-well were plated onto pre-coated poly-L-Ornithine/Laminin 6-well dishes (see Example 18) containing 3 glass slides (12 mm diameter) per well. A media change was performed every second day. Under these culture conditions the cells could be kept undifferentiated for at least 3 passages optionally more (see Example 16) and were also further processed for immunostaining to identify the neural progenitor cells using the procedure described in Example 16. The detachment with 1×PBS (Ca, Mg free), pH 7.4 is very efficient and selective for neural rosettes and eliminates the simultaneous harvesting of contaminating non-neural cells during the step. FIG. 14 shows plated neural progenitor cells after 3, 6 and 12 days of plating and FIG. 15 shows an immunocytochemical staining performed at day 6 after plating of the cells for the neural cell markers Nestin and Sox1.

Human ESCs that were initially subjected to medium mTeSR®1-F 270 mOsm/kg, and were dissociated into neural progenitor cells using 1×PBS (Ca, Mg free), pH 7.4, gave rise to typical rosette structures, which co-stained for Nestin and Sox1.

Neural progenitor cells co-expressing Sox1 and Nestin could not be obtained from attached EB colonies that were initially formed and cultured in mTeSR®1-F 340 mOsm/kg as described in Examples 6, 7 and 13.

To summarize the influence of media osmolality on germ layer induction and especially induction of ectodermal fate followed by selection of neural progenitor cells, Examples 12 and 13 clearly demonstrate that the osmolality of the medium used for EB formation and cultivation directs the germ layer fate undertaken by pluripotent human stem cells on their way to differentiating towards a mature cell type. Example 14 shows that those neural progenitor cells obtained in medium with an osmolality range of 260-280 mOsm/kg can be passaged selectively and cannot be obtained from EBs generated and grown in mTeSR®1-F 340 mOsm/kg, again underlining the effect of different osmolalities on cell fate determination.

Example 15 Selection of Neural Progenitor Cells from Neural Rosettes by a Mechanical Selection Procedure

To obtain a highly pure population of neural progenitor cells, neural rosettes were manually isolated from attached EB colonies (as generated in Example 11). For this purpose, a bent 26-gauge needle attached to a syringe was used. Rosettes were isolated by cutting an area with many rosettes present from the Poly-L-ornithine/laminin matrix using the needle and removing them from the dish with a 200 μl pipette tip. They were transferred into a sterile 1 ml tube. After pooling of all excised rosette structures, they were mechanically disrupted with a 200 μl pipette tip and plated onto a poly-L-ornithine/laminin coated dish (Example 18). Rosettes isolated from 2-3 single 6-wells were plated into one 6-well. This procedure gave rise to a highly pure population of neural progenitor cells, which formed small clusters containing rosettes as shown in FIG. 16 one day after plating them down onto poly-L-ornithine/Laminin (see Example 18) coated dishes. The neural progenitor cells within these clusters could then be further passaged and maintained according to the method described in Example 16.

Example 16 Method to Passage Neural Progenitor Cells

Various methods to passage neural progenitor cells are available. The method used below works in a consistent manner to generate single cell suspensions of neural cells. When cultured neural progenitor cells from Example 14 or 15 above reached 80-90% confluency (after 3-4 days), neural progenitor cells were passaged by brief exposure to 0.5% trypsin-EDTA (STEMCELL TECHNOLOGIES INC. catalogue #07910). The passaging is performed every 3-4 days and outlined below. For this step, medium was aspirated and the cells were washed once with 1×PBS (Ca, Mg free), pH 7.4. After aspirating the PBS, 500-600 μl of 0.5% trypsin-EDTA was added to a 6-well of neural progenitor cells. The dish was incubated at 37° C. until cells started lifting off the dish or for a maximum time of 5 minutes. Trypsin was inactivated by adding an equal volume of medium or 1×PBS (Ca, Mg free), pH 7.4 containing 10% of fetal bovine serum (STEMCELL TECHNOLOGIES INC. catalogue #06902). Cells were carefully triturated using a 5 ml serological pipette. The cell suspension was centrifuged at 300×g for 5 minutes. The supernatant was aspirated and the cell pellet was gently tapped to dislodge the cells. 500 μl of fresh culture medium were added (mTeSR®1-F 270 mOsm/kg+10 ng/ml bFGF) and the cells were triturated 2-4 times using a 1000 μl pipette tip. Cells were split at a 1:3 to 1:6 ratio. Media changes were performed every second day. FIG. 17 shows passaged neural progenitor cells at passage 1, 2 days after plating.

Example 17 Identification by Immunocytochemistry Based on Marker Expression of Neural Progenitor Cells Induced and Grown in mTeSR®1-F 270 and 340 mOsm/kg

Progenitor cells of ectodermal origin were induced to various extent as described in Examples 6, 7, 9, 11 and 13 using mTeSR®1-F 270 or 340 mOsm/kg. Disrupted EBs (see Example 11 and 13) were seeded onto 6-wells containing 3 glass coverslips (VWR microcoverglass, catalog #89015724) per well (coated with poly-L-ornithine/laminin). To assess the percentage of ectodermal and therefore neural progenitor cells, immunocytochemistry for neural markers was performed (FIG. 11). The presence of neural progenitor cells after selection and propagation (Example 14, 15 and 16; FIGS. 14 and 17 were also investigated. Optionally 2 days after the cells had been plated down, cells were washed once with 1×PBS (Ca, Mg free), pH 7.4 and the fixed with 4% paraformaldehyde for 20 minutes at room temperature. The coverslips were washed twice with 1×PBS (Ca, Mg free), pH 7.4 and were stored in 1×PBS (Ca, Mg free), pH 7.4 at 4° C. until immunocytochemistry was performed.

On the day of immunocytochemistry, cells were briefly rinsed with room temperature 1×PBS (Ca, Mg free), pH 7.4. Blocking solution consisting of 10% normal donkey serum (Jackson Immunoresearch Laboratories, catalog #017000121) and 0.2% Triton X (Sigma, catalog #T9284) was applied for 1 hour at room temperature with gentle shaking. Subsequently, the primary antibody solution containing the antibody in the appropriate concentration (see below) and 2% normal donkey serum was added for one hour at room temperature.

Antibodies were directed against Sox1 (goat α-Sox1, 1:200, Neuromics, catalogue #GT15208) and Nestin (mouse α-Nestin, 1:3000, Millipore, catalog #MAB5326) to identify early embryonic ectoderm. After incubation with the primary antibody, cells were washed 3×15 minutes with 1× PBS (Ca, Mg free), pH 7.4 at room temperature with gentle shaking. Primary antibodies were detected using secondary antibodies generated in donkey directed against the species the primary antibodies were of origin, conjugated to FITC (α-mouse) (Jackson Immunoresearch Laboratories, catalog #715095150; 1:500) or Texas red (α-goat) (Jackson Immunoresearch Laboratories, catalog #705075003; 1:500); by a 30-minute incubation step. To wash away unspecific binding, the cells were washed 3× using 1×PBS (Ca, Mg free), pH 7.4. To mount the coverslips, they were briefly dipped in distilled water. One drop of mounting solution containing DAPI (Vector laboratories, catalog #H-1500) was applied to the coverslip and with the cells facing downwards, the coverslip was mounted on a glass slide (Corning microslides, catalog #2947). After complete drying of the mounted coverslip on the glass slide, the immunfluorescence was visualized under a fluorescent microscope using the appropriate filters for each fluorophore. The co-expression of Nestin and Sox1 was observed in cells containing neural rosettes, which were induced and cultured in mTeSR®1-F 270 mOsm/kg as shown in FIG. 8. FIG. 11 shows co-expression of Nestin and Sox1 in neural progenitor cells cultured in mTeSR®1-F 270 mOsm/kg as compared to mTeSR®1-F 340 mOsm/kg. Attached EB colonies and neural progenitor cells induced in mTeSR®1-F 340 mOsm/kg, showed overall less staining with the 2 markers.

Example 18 Coating of Dishes with Poly-L-Ornithine/Laminin

In all previously described examples where cells or EBs were allowed to attach to a culture vessel, an extracellular matrix or combination of matrices were prepared prior to culture. For example, plastic polystyrene cell culture dishes as well as glass coverslips localized in either single wells of a 24-well plate or as triplicate in single 6-wells, were coated optionally with poly-L-ornithine/laminin. Briefly, plastic culture dishes or coverslips were covered with poly-L-ornithine (Sigma, catalog #P4957) optionally over night at least for 2 hours at room temperature. Dishes were washed twice with room temperature 1×PBS (Ca, Mg free), pH 7.4. The third wash consisted of sterile distilled water or DMEM/F12. Laminin (Sigma, catalog #L2020) at a concentration of 5 μg/ml was dissolved in ice-cold DMEM/F12. After aspirating off the water or DMEM/F12 from the dishes, using an ice-cold serological pipette, the laminin solution was added. 1 ml was used for a single 6-well or 500 μl for a single 24-well. Plates were placed at 37° C. for optionally 12 hours, at least 2.5 hours. Before plating cells, the laminin solution was discarded and medium added.

Example 19 Differentiation of Neural Progenitor Cells into Neurons and their Detection

Differentiation of neural progenitor cells was initiated by withdrawal of bFGF from the mTeSR®1-F 270 mOsm/kg medium and addition of factors such as but not limited to GDNF, cAMP. The cells were incubated with this medium for a minimum period of 5 days. Medium was changed every 2 days. FIG. 18 shows neurons stained (for immunocytochemical staining method see example 17) by the mature neuronal marker TUJ1. Neurons could only be derived from hESCs initially induced as EBs as described in Examples 7, 9 and 11 using mTeSR®1-F 270 mOsm/kg (left side of FIG. 18) and not from hESCs initially induced as EBs as described in Examples 7 and 13 using mTeSR®1-F 340 mOsm/kg (right side of FIG. 18).

Example 20 Culture of Human Pluripotent Stem Cells as Aggregates in Defined Serum-Free Medium on BD Matrigel™ Coating

Human pluripotent cells were maintained on BD Matrigel™ coated dishes in defined serum-free medium. A detailed protocol can be found in manual #29106 “Maintenance of hESCs AND hiPSCs in mTeSR®1 and TeSR™2” by STEMCELL TECHNOLOGIES INC. for the maintenance of human pluripotent stem cells which includes the procedure for BD Matrigel™ coating. The procedure described in this example for passaging the cells was applied for human embryonic stem cell lines H1 and H9 and for the human induced pluripotent stem cell line 4D1. Cells were passaged when the colonies were large, beginning to merge, and had centers that are dense and phase-bright compared to their edges (see FIG. 1). Depending on the size and density of seeded aggregates, cultures were passaged 5-7 days after initial seeding.

Medium was aspirated from the stem cell culture and cells were rinsed with DMEM/F-12 (2 mL/well). 1 mL of dispase (STEMCELL TECHNOLOGIES INC. catalogue #07923) was added per well at a concentration of 1 mg/mL. The dish was placed at 37° C. for 7 minutes.

Once the colony edges appeared slightly folded back, dispase was removed, and each well was gently rinsed 2-3 times with 2 mL of DMEM/F-12 per well to dilute away any remaining dispase. 2 mL/well of DMEM/F-12 or mTeSR®1 was added to the well and colonies were scraped off with a cell scraper (e.g. Corning Catalog #3010) or a serological pipette tip.

The detached cell aggregates were transferred to a 15 mL conical tube and the well was rinsed with an additional 2 mL of DMEM/F-12 to collect any remaining aggregates. The rinsed media containing remaining cells was added to the same 15 mL tube.

The 15 mL tube containing the aggregates was centrifuged at 300×g for 5 minutes at room temperature (15-25° C.). The supernatant was aspirated. For each well of hESC aggregates collected in the 15 mL tube, 1-2 mL of mTeS®1 were added. The pellet was resuspended gently by pipetting up and down using a P1000 micropipette (1-2 times). Cells were maintained as aggregates. Using the “clump count” method the number of clumps was estimated. To enumerate clumps that are likely to attach and grow of the right size (˜50-60 μm in diameter), a micrometer placed in the microscope eyepiece is used. To perform the clump count, 30 μL of DMEM/F-12 were aliquoted into 2 wells of a 96-well flat-bottom plate. A “+” was drawn centered on the bottom of these wells to serve as a counting grid. 5 μL of a freshly mixed clump suspension was added to each well. Clumps were counted in duplicate that were approximately 3500 μm² or greater. This corresponds to clumps with a diameter of approximately 60 μm. The total number of clumps per μl was estimated using the formula: Total # of clumps perμl=xclumps counted/5 μL total volume of suspension

A defined number of clumps according to the size of the well or dish that is being seeded was plated. The volume of clump suspension (y) used to seed new dishes was calculated using the guide in Table 1 for appropriate seeding densities. For example (y) for a 6-well equals: 350/#clumps counted per μl.

Human pluripotent stem cell aggregates were plated with 2 mL of mTeSR®1 per new 6-well coated with BD Matrigel™. The plate was moved in several quick, short, back-and-forth and side-to-side motions to disperse cells evenly across the surface of the wells. The plate was placed in a 37° C. incubator. The protocol above was applied to H1, H9 and 4D1 cells and cells were used as consistent cell source for the examples described in this disclosure.

FIG. 19 shows undifferentiated H1 hESCs (A) and 4D1 iPSCs (B) on day 5 of culture.

Example 21 Culture of Human Pluripotent Stem Cells as Single Cells in Defined Serum-Free Medium with BD Matrigel™ Coating

Human pluripotent stem cells were maintained on BD Matrigel™ coated 6-well dishes in defined serum-free medium such as mTeSR®1. In this example, the human embryonic stem cell line H9 cells was cultured as single cells and these cells were used for Example 37. The time of passaging was determined based on the confluency of cell colonies. Cell colonies reached approximately 70% confluency (FIG. 20A) 5 to 6 days of culture after the previous passage.

To passage cells, medium was aspirated from the stem cell culture and cells were rinsed with DMEM/F-12 (2 mL/well). 1 mL of Accutase (STEMCELL TECHNOLOGIES INC. catalogue #07920) was added per well. The dish was placed at 37° C. for 8-10 minutes until all cells detached.

5 ml of DMEM/F-12 was added to the Accutase and cell aggregates were dissociated into a single cell suspension using a 5 mL serological pipette. Cells were transferred to a 15 mL conical tube and the well was rinsed with an additional 2 mL of DMEM/F-12 to collect any remaining cells. The rinsed media containing remaining cells was added to the same 15 mL tube.

The 15 mL tube containing the single cell suspension was centrifuged at 300×g for 5 minutes at room temperature (15-25° C.). The supernatant was aspirated. Stem cells collected from each well and then transferred to the 15 mL tube were routinely resuspended in 1-2 mL of mTeS®1. The pellet was resuspended gently by pipetting up and down using a P1000 micropipette (1-2 times). Viable cells were counted using standard techniques, by diluting a 10 μL sample of the cell suspension 1:10 in 90 μL of trypan blue (Invitrogen, catalog #15250061) and counting unstained cells on a haemocytometer. The number of cells per μl allows calculation of the volume of cells to be plated into fresh Matrigel™ coated 6-well dishes. Cells were plated either at a density of 3×10³-5×10³ cells per cm² with Y27632 rock inhibitor (STEMCELL TECHNOLOGIES INC. catalogue #07171/2) at a final concentration of 10 μg/mL to enhance cell survival after plating (Watanabe et al, 2007) or without Y27632 at a density of 2×10⁴-5×10⁴ per cm². FIG. 20 (C) shows pluripotent stem cells (H9) plated at a density of 2×10⁴ per cm² one day after plating.

Example 22 Morphological Assessment of Pluripotency of Human Pluripotent Stem Cell Lines Grown as Aggregates or Single Cells in mTeSR®1 on BD Matrigel™

For the successful induction of germ layers, a highly pure population of pluripotent stem cells was used. For the following examples, the human embryonic stem cell lines H1, H9 and the human induced pluripotent cell line 4D1 were used. The following criteria were employed to assess the morphology and quality of cells (described in technical manual #29106 by STEMCELL TECHNOLOGIES INC.): Undifferentiated human pluripotent stem cells, grew as compact, multi-cellular colonies, as shown in FIGS. 1 and 19. They exhibited a high nuclear-to-cytoplasm ratio and prominent nucleoli. These colonies were characterized by a distinct border. Healthy hESC (and iPSC) colonies were multilayered in the center, resulting in clusters of phase-bright cells when viewed under phase contrast. Differentiation was characterized by loss of border integrity, gross non-uniform cell morphology within the colony and the emergence of obvious alternate cell types. The percentage of colonies displaying differentiated cell types was estimated by observation of the colonies under the microscope (using 4× and 10× objectives). For efficient induction of germ layers, cultures that displayed less than 15% of differentiated colonies were used in the following examples with exception of Example 37 where cultures with 40-50% of differentiation were used.

The criteria to assess pluripotency was used for human pluripotent stem cells cultured as aggregates (Example 20) as well as cells cultured as single cells (Example 21).

Example 23 Media Formulations with Different Osmolality Ranges Factor Free mTeSR®1 Medium at an Osmolality of 270 mOsm/kg

The complete media formulation and method of preparation for modified TeSR (mTeSR®1, STEMCELL TECHNOLOGIES INC., catalogue #05850) is published in Ludwig et al, Nature Methods 3(8): 637, 2006. It is based on the original TeSR formulation published in Ludwig et al., Nature Biotechnology 24(2): 185, 2006, with the following modification: substitution of human serum albumin (HSA) with bovine serum albumin (BSA).

To manufacture the factor free mTeSR®1 (mTeSR®1-F) media, a 5× supplement was produced containing all of the mTeSR®1 reagents at 5-fold concentrations, with the exceptions of the following 5 factors: GABA, pipecolic acid, bFGF, TGFβ1, lithium chloride. The components for the media are shown in Table 2.

After mixing the components of the 5× supplement together, the pH was adjusted to 7.4 by adding 10N NaOH. The osmolality of the solution was measured using a standard osmometer. The initial osmolality of the 5× supplement was usually around 100 mOsm/kg, and salt (NaCl) was used to increase the osmolality while taking into account that the 5× supplement is combined with 400 ml of the base medium DMEM/F12 (Hyclone, catalog #SH30004) to obtain mTeSR®1-F. The amount of salt that had to be added to the 5× supplement was calculated using the following formula: To obtain an osmolality of 270 after mixing the 5× supplement and the basal medium: [270−((0.8×300 mOsm)+(0.2×100 mOsm))]/2000×58.44×1.05=0.30 g/L of NaCl

The x amount of NaCl was added to the 5× supplement to obtain mTeSR®1-F 270 mOsm/kg.

Example 24 Generating a Single Cell Suspension of Human Pluripotent Cells for EB Formation in AggreWell™800

The procedure to generate single cells from human pluripotent stem cells and using them in the AggreWell™800 protocol and device is described in technical manual 29146 (STEMCELL TECHNOLOGIES INC.). The human pluripotent stem cell lines that were dissociated into single cell suspensions and were used to set up EBs in AggreWell™800 in the following examples were human embryonic stem cell lines H1, H9 and induced pluripotent stem cell line 4D1. The details how to obtain a single cell suspension from pluripotent stem cells are described in Example 6. In this example, the medium used to resuspend the cells was mTeSR®1-F 270 mOsm/kg (see Example 23). Setting up EBs in AggroWell™800 is described in the following example.

Example 25 EB Formation from Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Using a Microwell Device (AggreWell™800) and Subsequent Suspension Culture in the Same Medium

Single cell suspensions of human pluripotent stem cells (in this example the human induced pluripotent stem cell line 4D1 was used) were obtained as described in Example 24. Here, EBs with a size of 2000 cells per EB were generated in AggreWell™800. In general, EBs ranging from sizes of 1000 cells to 20000 cells can be generated in AggreWell™800. The plate was prepared as described in Example 7. Compared to an AggreWell™400 well, a single well of on AggreWell™800 plate contains approximately 300 microwells. As shown in table 3, 600,000 cells needed to be added to each well of the plate to obtain EBs with 2,000 cells in AggreWell™800. The volume of the single cell suspension generated in Example 22 containing 600,000 cells was determined based on the cell counts obtained (for cell counting see Example 6). This volume was added to each well of the AggreWell™800 plate previously prepared (see Example 7). The medium used in this example was mTeSR®1-F with an osmolality of 270 mOsm/kg. The cell suspension was distributed into the ˜300 microwells of an AggreWell™800 plate. Medium was added to a final volume of 2 mL per well. The AggreWell™800 plate was centrifuged at 100×g for 3 minutes to capture the cells in the microwells. Plates were incubated at 37° C. with 5% CO₂ and 95% humidity for 24 hours.

After 24 hours, EBs were harvested by gently pipetting up and down the medium in the AggreWell™800 microwells−2-3 times with a 1 mL disposable pipette tip to dislodge most of the EBs. To harvest the EBs, the suspension was passed through an inverted 40 μm nylon cell strainer (Falcon) sitting on top of a 50 mL conical tube to remove single cells and debris. The AggreWell™800 surface was washed a further 5-10 times with 1 mL each of DMEM/F-12, pipetting across the entire surface to dislodge all aggregates. All washes were applied onto the cell strainer membrane. The cell strainer was turned upside down, holding it close over a low-adherence 6-well. EBs were washed of the membrane using mTeSR®1-F 270 mOsm/kg medium. Approximately 5 ml of medium were used to remove the EBs from the nylon membrane holding the strainer over a single well of a 6-well ultra-low adherence dish (STEMCELL TECHNOLOGIES INC., catalog #27145). EBs were incubated in a standard tissue culture incubator, at 37° C., 5% CO₂ and 95% humidity for a period of 5 days, with a media change every 2-3 days. For this purpose, the dish was tilted towards one side and using a 1000-μl pipette tip, approximately half the volume of the medium was removed without disturbing the EBs. Fresh medium was added up to 5 ml. FIG. 21 shows EBs generated from 4D1 pluripotent stem cells inside the microwells of an AggreWell™800 plate after 24 hours before harvest (4× and 10× magnification) and the released EBs after 2 days and 4 days in suspension culture at 2× and 10× magnification.

Example 26 EB Formation from Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Using a Microwell Device (AggreWell™800), Subsequent Suspension Culture Followed by Plating of EBs to Obtain Neural Ectoderm

Single cell suspensions were obtained from human induced pluripotent stem cell line 4D1 as described in Example 24 and EBs were set up in AggreWell™800 in mTeSR®1-F with an osmolality of 270 mOsm/kg and were cultured in suspension culture as described in Example 25. EBs were plated after 5 days onto Poly-L-ornithine/Laminin coated 6-well plates (see Example 18 for coating of plates and Example 11 for the procedure for dissociation of EBs and subsequent plating the dissociated EBs). Three days after plating, the presence of ectoderm was assessed using the methods of Example 12. FIG. 22 shows neural rosettes in the attached plated EBs formed at a size of 2000 cells per EB from the human induced stem cell line 4D1.

Example 27 The Induction of Neural Ectoderm from Human Pluripotent Stem Cells in a Microwell Device (Aggrewell™800) Containing mTeSR®1-F with an Osmolality of 270 mOsm/Kg or mTeSR®1 with an Osmolality of 340 mOsm/kg Followed by Subsequent Culture and Plating of EBs in the Same Media

Single cell suspensions were obtained from human induced pluripotent stem cell line 4D1 and human embryonic stem cell line H9 as described in Example 24. EBs were set up in AggreWell™800 as described in Example 25 with the exception of using two different media: mTeSR®1-F with an osmolality of 270 mOsm/kg and 340 mOsm/kg. EBs from 4D1 cells were set up in both media at a size of 2000 cells per EB using the calculations in Table 3. EBs from H9 cells were set up at a size of 5000 cells using the methods described in Examples 24 and 25 and calculations for EB size provided in Table 3 in both media: mTeSR®1-F with an osmolality of 270 mOsm/kg and 340 mOsm/kg. EBs were harvested from the microwell device after 24 hours as described in Example 25 with the difference to the protocol that a different technique was used to dislodge the EBs from the microwells for EBs containing 5000 cells per EB. To dislodge EBs larger than 3000 cells, large bore tips (e.g. Rainin Catalog #HR-1000 WS) or regular 1000 μl disposable pipette tips where the tip has been aseptically cut off to increase the bore size. In addition, to increase recovery of EBs from the AggreWell™800 wells, a regular 1000 μl disposable tip was used to dislodge the EBs and the wider (cut) tip was used to collect the EBs onto the cell strainer (see Example 25).

EBs were cultured in suspension culture as described in Example 25 and were plated after 5 days onto Poly-L-ornithine/Laminin coated 6-well plates (see Example 18 for coating of plates and Example 11 for plating the EBs down). 4 to 5 days after plating, the presence of ectoderm was assessed using the methods of Example 12. FIG. 23 shows neural rosettes in the attached plated EBs formed from both cell lines (H9 A-D, 4D1 E-H) in both media. To the experienced eye, there are clearly more neural rosettes present in medium mTeSR®1-F with an osmolality of 270 mOsm/kg compared to mTeSR®1-F with an osmolality of 340 mOsm/kg. Scoring of the neural rosettes was performed as described in Example 12 (4D1 attached EBs were scored at day 4, H9 attached EBs were scored at day 5) and shows higher percentages of neural rosette containing (colony displaying more than 50% of area covered by neural rosettes) colonies in mTeSR®1-F with an osmolality of 270 mOsm/kg compared to mTeSR®1-F with an osmolality of 340 mOsm/kg. The scoring results are also indicated in FIG. 23.

Example 28 Continual Culture of EBs of Different Sizes Within Microwell Device (AggreWell™400) in mTeSR®1-F with an Osmolality of 270 mOsm/kg for 5 Days to Induce Ectoderm

A single cell suspension from the human embryonic stem stem cell line H9 was obtained as described in Example 6. EBs were set up as described in Example 7 with the exception that only mTeSR®1-F with an osmolality of 270 mOsm/kg was used. Different sizes of EBs were formed: 500 cells, 1000 cells and 2000 cells. Single cell suspension volumes which were added to the AggreWell™400 wells were calculated according to cell counts and the numbers given in Table 3. In this example, instead of harvesting the EBs from the AggreWell™400 plate after 24 hours (see Example 9) the EBs were left in the microwells for up to 11 days. Medium was changed every day by removing approximately 1.5 mL of media from an individual AggreWell™400 well using a micropipettor outfitted with a disposable 1 mL tip. Pre-warmed (37° C.) fresh mTeSR®1-F 270 mOsm/kg medium was dispensed slowly into the well thereby making sure not to disturb the EBs in the microwells.

Example 29 Induction of Neural Ectoderm from Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Using a Microwell Device (AggreWell™400) to Generate EB of Different Sizes, Culture of EBs Within the Same Device and Plating of EBs

As described in Example 27, EBs of various sizes (500, 1000 and 2000 cells per EB) were set up from the human embryonic stem cell line H9. EBs were cultured in the microwell device AggreWell™400 in mTeSR®1-F 270 mOsm/kg for 5 days. To release EBs in order to plate them down, the same methods described in Example 9 were used, with the exception that EBs were not plated onto ultra low adherence plates but instead directly onto 6-well plates coated with Poly-L-ornithine/Laminin (see Example 18). 2 mL of medium was used to wash the EBs from the cell strainer (Falcon) (see Example 9). The 6-well plates were agitated in a backward and forward manner to distribute the EBs evenly across the surface. Plates were placed into an incubator 37° C. with 5% CO₂ and 95% humidity for at least 2 days before morphological assessment. Morphological assessment of neural rosettes representing ectoderm was performed as described in Example 12. FIG. 24 shows attached EBs of various sizes (500 cells per EB (A,B), 1000 cells per EB (C,D), 2000 cells per EB (E,F)) 1 day after plating. To a person skilled in the art the neural rosettes are present to an extent of nearly 100% in all attached EBs.

Example 30 Highly Efficient Neural Ectoderm Induction of Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Compared to mTeSR®1-F with an Osmolality of 340 mOsm/kg with EB Formation and Continual Culture in a Microwell Device (AggreWell™400) and Subsequent Plating of EBs to Induce Ectoderm

EBs were formed and cultured in AggreWell™400 from human embryonic stem cell line H9 as described in Example 7. Media used in this example were mTeSR®1-F with an osmolality of 270 and 340 mOsm/kg. Two different sizes of EBs were set up: 500 cells per EB and 2000 cells per EB. EBs were cultured in the microwell device for 5 days and then plated as described in Example 29. FIG. 25 shows the morphology of plated EBs at day 2 in both media at two different sizes as well as scoring results (colonies with >50% of area containing rosettes). The results indicated that the induction of neural ectoderm from human pluripotent stem cells in mTeSR®1-F with an osmolality of 270 mOsm/kg was more efficient than in mTeSR®1-F with an osmolality of 340 mOsm/kg.

Example 31 Continual Culture of EBs of Different Sizes Within Microwell Device (AggreWell™800) in mTeSR®1-F with an Osmolality of 270 mOsm/kg for 5 Days to Induce Ectoderm

A single cell suspension from the human embryonic stem stem cell line H9 was obtained as described in Example 24. EBs were set up as described in Example 25 with the exception that only mTeSR®1-F with an osmolality of 270 mOsm/kg was used. Different sizes of EBs were formed in AggreWell™800: 2000 cells, 5000 cells, 10000, 15000 and 20000 cells. Single cell suspension volumes, which were added to the AggreWell™800 wells were calculated according to cell counts and the numbers given in Table 3. In this example, instead of harvesting the EBs from the AggreWell™800 plate after 24 hours, the EBs were left in the microwells for up to 11 days. Medium was changed every day by removing approximately 1.5 mL of media from an individual AggreWell™800 well using a micropipettor outfitted with a disposable 1 mL tip. Pre-warmed (37° C.) fresh mTeSR®1-F 270 mOsm/kg medium was dispensed slowly into the well thereby making sure not to disturb the EBs in the microwells.

Example 32 Induction of Neural Ectoderm from Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/Kg Using a Microwell Device (AggreWell™800) for EB Formation and Culture Within the Same Device Followed by Plating of the EBs

As described in Example 31, EBs of various sizes were set up from the human embryonic stem cell line H9. EBs were cultured in the microwell device AggreWell™800 in mTeSR®1-F 270 mOsm/kg for 5 days. To release EBs in order to plate them down, the same methods described in Example 27 were used for EBs larger than 3000 cells per EB, with the exception that EBs were not plated onto ultra low adherence plates but instead directly onto 6-well plates coated with Poly-L-ornithine/Laminin (see Example 18). 2 mL of medium was used to wash the EBs from the cell strainer (Falcon). The 6-well plates were agitated in a backward and forward manner to distribute the EBs evenly across the surface. Plates were placed into an incubator 37° C. with 5% CO₂ and 95% humidity for at least 2 days before assessing the cultures morphologically. Morphological assessment of neural rosettes representing ectoderm was performed as described in Example 12. FIG. 26 shows attached EBs of various sizes inside the microwells of AggreWell™800 at day 5 before releasing and plating the EBs. FIG. 27 shows EBs 1 day after plating. To the experienced eye the neural rosettes are present to an extent of nearly 100% showing that mTeSR®1-F 270 mOsm/kg can induce neural ectoderm at very high efficiency in AggreWell™800 when using different numbers of human pluripotent stem cells for EB formation as well as continuous culture inside the microwells.

Example 33 Highly Efficient Neural Ectoderm Induction of Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Compared to mTeSR®1-F with an Osmolality of 340 mOsm/kg with EB Formation and Culture in a Microwell Device (AggreWell™800)

EBs were formed and cultured in AggreWell™800 from human embryonic stem cell line H9 as described in Example 31. Media used in this example were mTeSR®1-F with an osmolality of 270 and 340 mOsm/kg. Two different sizes of EBs were set up: 2000 cells per EB and 5000 cells per EB. EBs were cultured in the microwell device for 5 days and then plated as described in Example 31. FIG. 28 shows the morphology of plated EBs at day 2. The results indicated that the induction of neural ectoderm from human pluripotent stem cells in mTeSR®1-F with an osmolality of 270 mOsm/kg was more efficient than in mTeSR®1-F with an osmolality of 340 mOsm/kg.

Example 34 Media Formulations with Different Osmolality Ranges Factor Free mTeSR®1 Medium with the Osmolalities 400 mOsm/kg and 450 mOsm/kg

The complete media formulation and method of preparation for modified TeSR (mTeSR®1, STEMCELL TECHNOLOGIES INC., catalogue #05850) is published in Ludwig et al, Nature Methods 3(8): 637, 2006. It is based on the original TeSR formulation published in Ludwig et al., Nature Biotechnology 24(2): 185, 2006, with the following modification: substitution of human serum albumin (HSA) with bovine serum albumin (BSA).

To manufacture the factor free mTeSR®1 (mTeSR®1-F) media, a 5× supplement was produced containing all of the mTeSR®1 reagents at 5-fold concentrations, with the exceptions of the following 5 factors: GABA, pipecolic acid, bFGF, TGFβ1, lithium chloride. The components for the media are shown in Table 2.

After mixing the components of the 5× supplement together, the pH was adjusted to 7.4 by adding 10N NaOH. The osmolality of the solution was measured using a standard osmometer. The initial osmolality of the 5× supplement was usually around 100 mOsm/kg, and salt (NaCl) was used to increase the osmolality while taking into account that the 5× supplement is combined with 400 mL of the base medium DMEM/F12 (Hyclone, catalog #SH30004) to obtain mTeSR®1-F. The amount of salt that had to be added to the 5× supplement was calculated using the following formula: For example to obtain an osmolality of 400 after mixing the 5× supplement and the basal medium: [400−((0.8×300 mOsm)+(0.2×100 mOsm))]/2000×58.44×1.05=4.3 g/L of NaCl

The x amount of NaCl was added to the 5× supplement.

Two media with different osmolalities were prepared: 400 mOsm/kg and 450 mOsm/kg.

Example 35 Highly Efficient Neural Ectoderm Induction of Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Compared to mTeSR®1-F with an Osmolality Range of 320, 340, 400 and 450 mOsm/kg in AggreWell™400

Single cell suspensions were obtained from H9 hESCs described in Example 6. EBs were formed in AggreWell™400 as described in Example 7. Media used for EB setup were mTeSR®1-F with osmolalities of 270 (Example 23), 320, 340 (Example 5), 400 and 450 mOsm/kg (Example 34). Y27632 rock inhibitor was also added to the medium at a final concentration of 10 μg/mL to enhance cell survival during EB formation. EBs with a size of 2000 cells per EB were set up and either taken out after 24 hours (see Example 9) and cultured in suspension culture until plating by trituration (see Example 11) or left in the AggreWell™ plates for 5 days and then plated (see Example 29).

FIG. 29 shows EB attachment after 2 days in the different media except in medium mTeSR®1-F 450 mOsm/kg. The EBs formed in this medium are shown at day 1. The percentage of rosettes was highest (100%) in medium with the osmolality of 270, with a drop at 320 and 340 and no rosettes formation observed in 400 and 450 mOsm/kg. Note that at an osmolality higher than 340, cell detachment and cell death was observed after plating and no morphologically distinct cell types could be identified. FIG. 30 shows the scoring results of these two experiments. Colonies with >50% of area containing rosettes were counted as well as all colonies. The ratio as well as the resulting percentage of rosette containing colonies is shown. Visual inspection of the 450 mOsm/kg condition on day 1 did not reveal any rosettes.

Example 36 Highly Efficient Neural Ectoderm Induction of Human Pluripotent Stem Cells Maintained as Single Cell Cultures in mTeSR®1-F with an Osmolality of 270 mOsm/kg Compared to mTeSR®1-F with an Osmolality of 340 mOsm/kg with EB Formation and Culture in a Microwell Device (AggreWell™800)

The human embryonic stem cell line H9 was passaged as single cells in culture for 4 passages between passage 51 to passage 55 (p51 to p55) as described in Example 21. Single cell suspensions of H9 obtained at passage 55 as described in Example 24 for EB formation in AggreWell™800. EBs were formed and harvested as described in Examples 31 and 32. FIG. 31 shows that neural rosettes are more efficiently formed in mTeSR®1-F 270 mOsm/kg (A) compared to mTeSR®1-F 340 mOsm/kg (B). This shows that medium with an osmolality of 270 mOsm/kg can efficiently induce neural ectoderm in human pluripotent stem cells cultured either as aggregates or single cells.

Example 37 Efficient Induction of Neural Ectoderm Using the Microwell Device (AggreWell™800) Containing mTeSR®1-F 270 mOsm/kg Compared to mTeSR®1-F 340 mOsm/kg from Human Pluripotent Stem Cell Cultures Displaying High Percentages of Differentiation

EBs were formed from H9 cell cultures which displayed between 40 and 50% of differentiation. Cells were morphologically accessed for differentiation as described in Example 22. FIG. 32 shows H9 cells at passage 52 (H9p52) at day 5 of culture after passaging and before EB set up (A-D). Differentiated areas are circled. Single cells for EB formation were obtained as described in Example 24 and EBs were formed in AggreWell™800 as described in Example 25. EBs were cultured and plated as described in Examples 31 and 32. Morphological assessment of neural rosettes was performed 2 days after plating as described in Example 12. FIG. 32 also shows morphology of EBs at day 2 after plating as well as scoring results (colonies with >50% area containing rosettes) (E-H, EBs set up in mTeSR®1-F 270 mOsm/kg (E,F); EBs set up in mTeSR®1-F 340 mOsm/kg (G,H). The results indicated that the induction of neural ectoderm from human pluripotent stem cells in mTeSR®1-F with an osmolality of 270 mOsm/kg was more efficient than in mTeSR®1-F with an osmolality of 340 mOsm/kg even if the percentage of pluripotent cells in the starting population is less than 85%, which is the percentage of colonies containing undifferentiated cells used as a cut-off for all other examples described in this disclosure.

Example 38 Efficient Induction of Neural Ectoderm from Human Embryonic Stem Cell Line H7 Using the Microwell Device (AggreWell™800) Containing mTeSR®1-F 270 mOsm/kg Compared to mTeSR®1-F 340 mOsm/kg

The hESC line H7 was cultured and passaged as described in Example 20. EBs were formed and cultured from p38 cells in AggreWell™800 using mTeSR®1-F 270 mOsm/kg or mTeSR®1-F 340 mOsm/kg as described in Example 30 with the exception that 5000 cells per EB were used. EBs were released from the microwells and plated as described in Example 31. FIG. 33 shows attached EBs 1 day after they have been plated. Morphological assessment for the presence of neural ectoderm was carried out as described in Example 12. More neural rosettes are present when EBs were formed and cultured in mTeSR®1-F 270 mOsm/kg compared to mTeSR®1-F 340 mOsm/kg.

Example 39 Efficient Induction of Neural Ectoderm from Human Pluripotent Stem Cell Cultures in Knockout™ D-MEM 270 mOsm/kg Compared to Knockout™ D-MEM 340 mOsm/kg Using the Microwell Device AggreWell™400 for Both EB Formation and Culture

EBs were formed and cultured in AggreWell™400 from human embryonic stem cell line H9 (p44) as described in Example 28. Media used in this example were Knockout™-D-MEM (Invitrogen Cat. No. 10829-018) with an osmolality of either 270 or 340 mOsm/kg adjusted using sodium chloride as described in Examples 5 and 22 (the standard osmolality of Knockout™-D-MEM is approximately 265 mOsm/kg). EBs comprising 2000 cells per EB were formed in Knockout™-D-MEM 270 mOsm/kg and Knockout™-D-MEM 340 mOsm/kg. EBs were cultured in the AggreWell™400 for 5 days and then collected and plated as described in Example 29. FIG. 34 shows the morphology of plated EBs at day 2. Morphological assessment of the plated EBs by identification of rosette structures showed that the induction of neural ectoderm from human pluripotent stem cells cultured in Knockout™-D-MEM with an osmolality of 270 mOsm/kg was more efficient compared to Knockout™-D-MEM with an osmolality of 340 mOsm/kg. Scoring for neural rosettes was performed as described in Example 12 at day 6 and the percentages are indicated in FIG. 34. The results indicated that Knockout™-D-MEM with an osmolality of 270 mOsm/kg is more potent at inducing neural rosettes compared to Knockout™-D-MEM with an osmolality of 340 mOsm/kg. Therefore an osmolality of 270 mOsm/kg adjusted even in an alternate media formulation such as Knockout™-D-MEM supported efficient neural ectoderm induction from human pluripotent stem cells.

Example 40 Efficient Induction of Neural Ectoderm from Human Pluripotent Stem Cell Cultures Cultured in Neurobasal™ Medium at an Osmolality of 270 mOsm/Kg Compared to Neurobasal™ Medium at an Osmolality of 340 mOsm/kg Using AggreWell™400 for EB Formation and Culture

EBs were formed and cultured in AggreWell™400 from human embryonic stem cell line H9 (p44) as described in Example 28. The media used in this example were Neurobasal™ medium (Invitrogen Cat. No. 21103049) with an osmolality of 270 or 340 mOsm/kg that was adjusted using sodium chloride as described in Examples 5 and 22 (the standard osmolality of Neurobasal™ medium is approximately 220 mOsm/kg). EBs comprising 2000 cells per EB were set-up in Neurobasal™ medium 270 mOsm/kg and Neurobasal™ medium 340 mOsm/kg. EBs were cultured in the microwell device for 5 days and then plated as described in Example 29. FIG. 35 shows the morphology of EBs inside the microwells of an AggreWell™400 plate on day 5 and EBs 2 days after they have been harvested and plated. Inside the microwells as well as in attached EBs, more rosettes are visible in Neurobasal™ medium 270 mOsm/kg than in Neurobasal™ medium 340 mOsm/kg. The results showed that the induction of neural ectoderm from human pluripotent stem cells in Neurobasal™ with an osmolality of 270 mOsm/kg was more efficient than in Neurobasal™ with an osmolality of 340 mOsm/kg. Scoring of rosettes was performed on day 6 after plating as described in Example 12 and reveals higher percentages of neural rosettes for Neurobasal™ with an osmolality of 270 mOsm/kg. Therefore other media formulations with an osmolality of 270 mOsm/kg are also useful to efficiently induce neural ectoderm.

Example 41 Superior Induction of Neural Ectoderm from Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Compared to mTeSR®1-F with an Osmolality of 340 mOsm/kg Prepared with 2 Different Lots of Bovine Serum Albumin (BSA)

Different lots of BSA lots were sourced and used to prepare the media formulations mTeSR®1-F 270 mOsm/kg and 340 mOsm/kg for the induction of neural ectoderm. As described in Examples 28 and 30, EBs containing 500, 2000 and 5000 cells per EB were generated from the human embryonic stem cell line H9 (p41, p45 and p44 respectively) using either AggreWell™400 or AggreWell™800. EBs were cultured in AggreWell™400 (500 cells/EB) or AggreWell™800 (2000 and 5000 cells/EB) in mTeSR®1-F (BSA lot 2 or lot 3) 270 mOsm/kg or mTeSR®1-F (BSA lot 2 or lot 3) 340 mOsm/kg for 5 days. EBs were released and plated using the same methods described in Examples 29 and 31. Morphological assessment by identifying neural rosettes was performed as described in Example 12. FIG. 36 shows attached EBs 3 days after plating. To a person skilled in the art it becomes obvious that there are higher quantities of rosettes formed in mTeSR®1-F (BSA lot 2 or lot 3) 270 mOsm/kg compared to mTeSR®1-F (BSA lot 2 or lot 3) 340 mOsm/kg and with rosettes being more morphologically distinguishable in the low osmolality medium. Furthermore, scoring of attached EBs on day 3 cultured in mTeSR®1-F 270 mOsm/kg containing BSA lot 3 reveals a higher percentage of neural rosettes compared to mTeSR®1-F 340 mOsm/kg containing BSA lot 3. Therefore media with an osmolality of 270 mOsm/kg induces efficient neural induction and rosette formation.

Example 42 Efficient and Consistent Induction of Neural Ectoderm from Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Containing BSA Lot 2 Using Either AggreWell™400 or 800 to Generate and Culture EBs of Various Sizes

As described in Example 30, EBs of different sizes (2000, 5000 and 10000 cells/EB) were formed in AggreWell™800 from the human embryonic stem cell line H9 (p44 and p53). Also EBs containing 2000 cells were formed in AggreWell™400 from human ESC line H1p59 as described in Example 28. EBs were cultured for 5 days in these AggreWell™ microwell devices in mTeSR®1-F (containing BSA lot 2) with an osmolality of 270 mOsm/kg. EBs were released for subsequent plating according to methods described in Examples 29 and 31. Morphological assessment by presence of neural rosettes representing ectoderm was performed as described in Example 12. Virtually 100% of rosettes were present in attached EB cultures. FIG. 37 shows attached EBs of different sizes 2 days after plating. These results clearly indicated that the induction of neural ectoderm in EBs that are formed and cultured in either AggreWell™800 or AggreWell™400 containing mTeSR®1-F with an osmolality of 270 mOsm/kg containing BSA lot 2 is highly efficient and consistent (n=20 experiments).

Example 43 Greater Efficiency in Induction of Neural Ectoderm from Human Pluripotent Stem Cells Cultured in TeSR™2 Using mTeSR®1-F 270 mOsm/kg Compared to mTeSR®1-F 340 mOsm/kg with Use of AggreWell™400 to Generate and Culture EBs

As described in Example 28, EBs containing 2000 cells per EB were formed in AggreWell™400 from the human embryonic stem cell line H9 (p52) previously cultured and maintained in TeSR™2 (STEMCELL TECHNNOLOGIES INC. catalog number 05860). EBs were formed in AggreWell™400 containing mTeSR®1-F with an osmolality of 270 mOsm/kg or 340 mOsm/kg and cultured for 5 days within the microwells. The method to release EBs and plate EBs is as in Example 29. Morphological assessment by presence of neural rosettes representing ectoderm was performed as described in Example 12. FIG. 38 shows attached EBs 2 days after attachment. Cells cultured in the medium with lower osmolality (270 mOsm/kg) produced more rosettes than cells cultured in the medium with high osmolality (340 mOsm/kg). Neural rosettes were also scored at day 2 and percentages are given in FIG. 38. EBs plated in medium with an osmolality of 270 mOsm/kg contained 90% rosettes compared to 18% rosettes in EBs plated in medium with osmolality of 340 mOsm/kg.

Example 44 Induction of Neural Ectoderm from TeSR™2 Cultured Human Pluripotent Stem Cells in mTeSR®1-F with an Osmolality of 270 mOsm/kg Compared to mTeSR®1-F with an Osmolality of 340 mOsm/kg (Both Media Containing BSA Lot 2) Using AggreWell™400 and AggreWell™800 to Generate and Culture EBs

In this example, the human embryonic stem cell line H9 (p64) which had been previously cultured and maintained in TeSR™2 (STEMCELL TECHNNOLOGIES INC. catalog number 05860) was used to generate EBs. EBs containing 2000 cells per EB were formed in AggreWell™400 in mTeSR®1-F (BSA lot 2) with an osmolality of 270 mOsm/kg or mTeSR®1-F (BSA lot 2) 340 mOsm/kg and cultured in the device for 5 days as described in Example 28. EBs with a size of 2000 cells per EB were also formed in AggreWell™800 EBs in both media described above and cultured in the device for 5 days as described in Example 30. The method to release and plate EBs is as described in Examples 29 and 31. Morphological assessment by presence of neural rosettes representing ectoderm was performed as described in Example 12. FIG. 39 shows attached EBs after they were released from either AggreWell™400 or AggreWell™800 and plated for 2 days. EBs were also scored for neural rosettes at day 2 and percentages are given in FIG. 39. EBs formed in the 270 mOsm/kg medium in either AggreWell™400 or AggreWell™800 contained rosettes in a range of 82-89%, EBs formed in 340 mOsm/kg medium in either AggreWell™400 or AggreWell™800 contained rosettes in a range of 41-46%. The results confirmed that osmolality of 270 mOsm/kg efficiently supports neural ectoderm induction.

Example 45 Highly Efficient Induction of Neural Ectoderm from TeSR™2 Cultured Human Pluripotent Stem Cells Using AggreWell™400 to Generate and Culture EBs in TeSR™2-F (Containing HSA) with an Osmolality of 270 mOsm/kg Compared to TeSR™2-F (Containing HSA) with an Osmolality of 340 mOsm/kg

In this example, the human embryonic stem cell line H9 (p52) which had been previously cultured and maintained in TeSR™2 (STEMCELL TECHNOLOGIES INC. catalog number 05860) was used to form EBs. EBs containing 2000 cells per EB were formed in AggreWell™400 in TeSR™2-F (containing HSA) with an osmolality of 270 mOsm/kg or 340 mOsm/kg and cultured in the microwells for 5 days as described in Example 28. The method to release and plate EBs is described in Example 29. Morphological assessment by presence of neural rosettes representing ectoderm was performed as described in Example 12. FIG. 40 shows attached EBs 2 days after attachment. The lower osmolality medium (TeSR™2-F (containing HSA) 270 mOsm/kg) contains more rosettes than the high osmolality medium (TeSR™2-F (containing HSA) 340 mOsm/kg). EBs were also scored at day 2 and percentages are given in FIG. 40. EBs set up in the lower osmolality (270 mOsm/kg) medium contain 23% rosettes, EBs set up in the higher osmolality (340 mOsm/kg) contain 5% rosettes.

In summary, the results showed that human pluripotent stem cells previously cultured and maintained in animal protein free medium (containing HSA) can also give rise to neural rosettes when cultured in mTeSR®1-F with an osmolality of 270 mOsm/kg or in TeSR™2-F with an osmolality of 270 mOsm/kg).

Example 46 Assessment of Induction of Neural Ectoderm in mTeSR®1-F Osmolality 270 mOsm/kg Compared to mTeSR®1-F Osmolality 340 mOsm/kg Containing Additional Supplements

EBs were formed from the hESC line H9 in AggreWell™400 or AggreWell™800 plates in mTeSR®1-F osmolality 270 mOsm/kg using protocols described in Example 9 and released after 24 hours as described in Example 11. Alternatively, they were formed and cultured inside the microwells of an AggreWell™800 plate in mTeSR®1-F with an osmolality 270 mOsm/kg as described in Example 30 and released as described in Example 31. Supplements were added to the medium during EB formation in the initial 24 hours of formation as well as to the ULA culture for 5 days or were added to the media changes when cells were cultured inside the microwells of an AggreWell™800 plate for 5 days. FIG. 41 shows EBs from ULA culture 6 days after they have been attached, formed and cultured in mTeSR®1-F with an osmolality 270 mOsm/kg and 20 ng/ml bFGF or 20 ng/ml bFGF and 1% B27 (Invitrogen, catalog number 0080085SA), 1% N2A (STEMCELL TECHNOLOGIES INC. catalog number 07152). The same figure shows EBs 4 days after attachment formed in mTeSR®1-F osmolality 270 mOsm/kg and cultured within the AggreWell™800 microwells for 5 days supplemented with 1% N2A, 100 ng/ml Fgf8/200 ng/ml shh or 1% B27. Other supplements used in this experiment (data not shown) were 2% and 5% BSA, 1% non essential amino acids (NEAA) (Invitrogen catalog number 11140050), Fgf8 (100 ng/ml) and shh (200 ng/ml) or 300 ng/ml Noggin (STEMCELL TECHNOLOGIES INC. catalog number 02525). Additional supplements include but are not limited to: SM1 (STEMCELL TECHNOLOGIES INC. Catalog number 05711), ascorbic acid, retinoic acid, cAMP, BDNF, forskolin, NeuroCult® Proliferation Supplements (STEMCELL TECHNOLOGIES INC. catalog number 05701), N2B (STEMCELL TECHNOLOGIES INC. catalog number 07156), Insulin-Transferin-Selenium (ITS) and other additives appropriate for neural progenitor cell expansion and differentiation.

Example 47 Efficient Induction of Neural Ectoderm in EBs Generated in mTeSR®1-F Osmolality 270 mOsm/kg Using AggreWell™800 and Plated at Different Time Points

As described in Example 30, EBs containing 2000 cells/EB were formed in AggreWell™800 from the human embryonic stem cell line H9 (p36 and p42). EBs were cultured in these AggreWell™ microwell devices in mTeSR®1-F with an osmolality of 270 mOsm/kg. EBs were released for subsequent plating according to methods described in Example 31 with the exception that EBs were harvested from the microwells at different time points (day 2, 3, 4, 5, 7, 8, 9 and 11). Morphological assessment by presence of neural rosettes representing ectoderm was performed as described in Example 12. FIGS. 42 and 43 show attached EBs released and plated at different time points, 1 to 5 days after plating. The attached EBs show a high content of neural rosettes when plated as early as day 1 after initial formation in AggreWell™800 3 days after plating (in total 4 days) or plated at day 2 and 1 day after plating (in total 3 days of induction in mTeSR®1-F 270 mOsm/kg). A mixture of rosettes of various sizes (circle in FIG. 43), single cell layer neural progenitor cells (thin arrow in FIG. 43) and mature neurons (thick arrow in FIG. 43) can be still identified in EBs plated as late as day 11 and analyzed 5 days after plating (in total 16 days after EB formation). This example shows that neural rosettes are induced as early as within 2 days in the AggreWell™800 plates and become obvious as early as 1 day after plating. When EBs are kept in the AggreWell™800 plates for 24 hours and are plated afterwards, then the plated EBs show rosettes within 3 days after plating of the EBs. EBs cultured in AggreWell™800 for up to 11 days, harvested and then cultured for 5 days (for a total of 16 days of culture in mTeSR®1-F 270 mOsm/kg), generated rosettes which contained neural cells with morphologies indicative of different stages of commitment to the neural fate (i.e. early neural progenitor cells were present in rosettes, single cell neural progenitor cells with bipolar morphology growing out from the rosettes and neurons with axonal projections) which can be identified by a person skilled in the art. Experiments were also performed for culturing EBs in the AggreWell™800 device containing mTeSR®1-F 270 mOsm/kg for a total of 6, 7, 9, 10 and 12 days. Furthermore, attached EB cultures were analyzed by flow cytometry analyses to determine the percentage of Sox1 positive neural progenitor cells (NPCs) in attached EBs plated after 1 or 5 days of culture within the AggreWell™800 microwells. The FACS plot in FIG. 42 shows that 35.21% of Sox1 positive cells were detected in attached EBs at 5 days compared to 0.77% Sox1 positive in EBs attached for 1 day.

Example 48 Efficient Neural Ectoderm Induction in EBs Formed and Cultured in mTeSR®1-F with an Osmolality of 270 mOsm/Kg in AggreWell™ and Plated onto Different Surfaces

EBs which contained 2000 cells per EB were formed from hESC line H9 p38 in AggreWell™800 as described in Example 30. EBs were released from AggreWell™ and plated onto Poly-L-ornithine/Laminin coated dishes as described in Example 31. Plates were coated as described in Example 18 with the exception that various concentrations of laminin were used: 1, 10 and 20 μg/mL. FIG. 44 shows EBs 3 days after attachment. 100% neural rosette formation is present in all conditions. Therefore, different concentrations of laminin allowed EB attachment at comparable efficiency.

Example 49 Culture of EBs Previously Formed in mTeSR®1-F with an Osmolality of 260 mOsm/kg or 270 mOsm/kg in Subsequent Neurosphere Suspension Cultures Leads to Highly Efficient Induction of Neural Rosettes and Neuronal Outgrowth after Plating

EBs were formed from H9 p51 hESCs in mTeSR®1-F with an osmolality of 260 mOsm/kg or 270 mOsm/kg in AggreWell™400 according to Example 9 and EBs were released from the microwells according to Example 11. As described in Example 51, attached EBs were dissociated with 1 mg/ml Dispase and re-plated. The next day many clumps of cells were present which had rounded up into aggregates or “neurospheres”. These neurospheres were transferred into Ultra Low Adherent (ULA) plates using a serological 5-mL pipette and cultured in the same medium they were previously cultured in (i.e. mTeSR®1-F with an osmolality of 260 mOsm/kg or 270 mOsm/kg) for 5 days. Neurospheres were then collected and plated onto Poly-L-ornithine/Laminin coated dishes (see Example 18). FIG. 45 shows neurospheres at day 1 after plating showing attached neurospheres formed in mTeSR®1-F with an osmolality of 270 mOsm/kg alone or containing 1% B27 (Invitrogen, catalog number 0080085SA) and/or 1% N2A (STEMCELL TECHNOLOGIES INC. catalog number 07152). Neurons (arrows), which extended projections, were observed in all 3 media. Other supplements (as described in Example 46) have also been used for the neurosphere culture medium. Alternatively, EBs kept in ULA culture in mTeSR®1-F with an osmolality of 260 mOsm/kg or 270 mOsm/kg for 13 days, harvested and plated for 6 days generated neural rosettes (thick arrows) and neurons (thin arrows) as shown in FIG. 46.

This example shows that culture of EBs formed in low osmolality media: mTeSR®1-F with an osmolality of 260 mOsm/kg or 270 mOsm/kg as neurospheres (after an initial passage and then transferred to ULA dishes) or culture of EBs for extended culture periods in ULA dishes leads to neuronal populations including rosettes and neurons.

Example 50 Pre-Conditioning of hPSC Cultures with mTeSR®1-F with an Osmolality of 270 mOsm/kg Prior to EB Formation in a Microwell Device Increase Efficiency of Neural Induction in mTeSR®1-F with an Osmolality of 320 mOsm

In this example hPSC lines were cultured in mTeSR® as described. Here, the hESC line H9 at passage 47 was used. Prior to EB formation the culture medium was changed to mTeSR®1-F with an osmolality of 320 mOsm/kg and cells were cultured for 24 hours. This step was performed to increase the efficiency of neural ectoderm formation particularly in the protocol described in Example 9. All EBs were formed in mTeSR®1-F with an osmolality of 270 mOsm/kg. Neural induction is assessed by neural rosette formation as described in example 12. EBs were formed from pre-conditioned H9 cells in AggreWell™400 as described in Example 9 and were released after 24 hours to be cultured in ULA plates for 5 days (as described in Example 11). FIG. 47 shows EBs 4 days after they were plated and allowed to attach onto Poly-L-ornithine/Laminin. Neural rosette percentages increased from 49% in non-conditioned medium (mTESR®1) (left picture) to 72% when hESCs were pre-conditioned in mTeSR®1-F with an osmolality of 320 mOsm/kg (right picture).

Example 51 Methods to Dissociate Attached EBs and Obtain Neural Progenitor Cells (NPCs)

As described in Example 9, EBs containing 2000 cells per EB were formed in AggreWell™400 from the human embryonic stem cell line H9 p47 in mTeSR®1-F with an osmolality of 270 mOsm/kg. EBs were released after 24 hours, cultured in ULA dishes and plated after 5 days of culture onto Poly-L-ornithine/Laminin as described in Example 11. Seven to 8 days after plating, the attached EBs were dissociated using various dissociation agents: cell dissociation buffer enzyme-free PBS based (Gibco, catalog number 13151-014), EDTA (0.02%), Dispase 1 mg/ml (STEMCELL TECHNOLOGIES INC., catalog number 07923), Accutase (STEMCELL TECHNOLOGIES INC., catalog number 07920), Neurocult® Chemical Dissociation Kit (Mouse) (STEMCELL TECHNOLOGIES INC., catalog number 05707) and Trypsin (0.05%) (Sigma, check). Attached EBs were dissociated in cell dissociation buffer enzyme-free PBS based (Gibco, catalog number 13151-014) at room temperature for 0.5 to 1 hour. The same incubation procedure was applied using 0.02% EDTA solution. After the incubation, cells were dissociated by trituration in the solutions (approx. 10 times using a P-1000 pipette tip). The culture dish was washed once with 1 mL of DMEM/F-12 with 15 mM HEPES (STEMCELL TECHNOLOGIES INC., catalog number 36254) and cells were centrifuged as described in Example 14. The supernatant was discarded and the cell pellet was dissociated with 2 mL of mTeSR®1-F with an osmolality of 270 mOsm/kg and plated on Poly-L-ornithine/laminin or matrigel (or other) coated 6-well plates. Cells were plated in various densities, and in this example a 1 to 1 split was performed. For dissociation with Dispase, 1 mL of a 1 mg/ml solution of Dispase was added to the attached EB cultures after the removal of induction medium (mTeSR®1-F with an osmolality of 270 mOsm/kg) from the culture. Plates were placed in a 37° C. incubator and cultures were observed until attached EB colonies started detaching from the plate. This step usually took between 10 and 40 minutes. Dispase was removed and the cells were washed 3 times with DMEM-F12. Trituration and centrifugation steps are described above and in Example 14. Accutase was added to the cells after the induction medium was discarded and cells were incubated until all the cells detached from the plate (usually 5-10 minutes) as per standard protocols. 5 mL of DMEM-F12 were added to the cells to inactivate the Accutase and cells were dissociated gently 1-2 times using a P-1000 pipette tip. Centrifugation and dissociation of the pellet as well as plating are described above. The Neurocult® Chemical Dissociation Kit (Mouse) was used as described on http://www.stemcell.com/en/Products/All-Products/NeuroCult-Chemical-Dissociation-Kit-Mouse.aspx (Manual: Chemical Dissociation of Neurospheres Derived from Adult and Embryonic Mouse CNS using the NeuroCult® Chemical Dissociation Kit—2009). Dissociated cells were centrifuged, the cell pellet dissociated as well as the cells plated as described above and in Example 14. For trypsin dissociation, trypsin was used at a concentration of 0.05% to dissociate attached EB cultures. After the culture medium was aspirated, cells were incubated with pre-warmed (to 37° C.) Trypsin at 37° C. for 1-2 minutes or until they started detaching from the dish. Trypsin was deactivated by addition of 1-2 mL of 10% ES-Cult® Fetal Bovine Serum for Neural Differentiation (STEMCELL TECHNOLOGIES INC., catalog number 06955) in D-PBS Without Ca++ and Mg++ (STEMCELL TECHNOLOGIES INC., catalog number 37350). Trituration, centrifugation and plating steps are described above. FIG. 48 shows NPCs dissociated using the various described reagents 4-6 days after plating. FIG. 49 shows NPCs 3 days after re-plating, which had been dissociated with either Accutase (this example), HBSS (Example 52) or PBS (Example 14), that were stained for the NPC marker Nestin and Sox1. Note that NPCs were also plated at different densities. This Example shows that attached EBs can be dissociated with various reagents and the resulting suspension containing NPCs are comparable to each other in term of morphology and marker staining.

Example 52 Efficient Isolation of Neural Progenitor Cells from Neural Rosettes within Attached EBs of Different Sizes Plated at Different Time Points

As described in Example 30, EBs containing 2000, 5000 and 10000 cells/EB were formed in AggreWell™ 800 from the human embryonic stem cell lines H7 and H9 (passages 38 or 35, 36, 41, 45, respectively). EBs were cultured for 5 days within AggreWell™ microwell devices in mTeSR®1-F with an osmolality of 270 mOsm/kg. EBs were released for subsequent plating according to methods described in Example 31 with the exception that EBs were harvested from the microwells at different time points (day 5, 6, 7, 9 and 11). FIG. 50 shows attached EBs (various sizes) at different time points (at day 5, 6 and 11) after releasing them from AggreWell™800 plates shown on the day the attached EBs were dissociated to obtain NPCs (only representative examples are shown). Neural rosettes were present in all conditions. NPCs were selectively isolated from attached EBs using the method described in Example 14 with the exception that in this example Hanks' Balanced Salt Solution (HBSS), calcium and magnesium free (Ca²⁺ and Mg²⁺) (Sigma catalog number C1419) was used. The cells were incubated for 0.5-2 hours at room temperature after the induction medium (mTeSR®1-F with an osmolality of 270 mOsm/kg) was discarded. Cells were dissociated and centrifuged as described in Example 14. The supernatant was removed and the cell pellet was dissociated with 2 mL of mTeSR®1-F with an osmolality of 270 mOsm/kg. NPCs were re-plated at various densities onto Poly-L-ornithine/Laminin (for coating procedure see Example 18). FIG. 51 shows isolated re-plated NPCs, at days 5 or 6 of culture, which were isolated from EBs plated at different time-points and also dissociated at different time-points. FIG. 52 shows NPCs 4 days after re-plating and also contains pictures of immunocytochemically (for method see Example 17) stained cells for markers of NPCs (PSA-NCAM, SOX1 and Nestin, as well as ZO-1, a tight junction protein and marker for the lumen of rosettes). For clarity, the table in FIG. 53 summarizes the individual experiments: the first column indicates the day the EBs were released from the AggreWell™800 plate. The second column indicates the day the attached EBs were dissociated, the third column indicates the number of days in total since formation of EBs in AggreWell™ and mTeSR®1-F 270 mOsm/kg, the fourth column indicates the size of the EB and the fifth column indicates the day the picture was taken with the total number of days the NPCs were in culture.

Example 53 Efficient Isolation of Neural Progenitor Cells from Neural Rosettes within Attached EBs and Culture of these Cells on Different Concentrations of Laminin

As described in Example 30, EBs containing 2000 cells/EB were formed in AggreWell™800 from the human embryonic stem cell line H9 (p65) EBs were cultured for 12 days in these AggreWell™ microwell devices in mTeSR®1-F with an osmolality of 270 mOsm/kg. EBs were released for subsequent plating according to methods described in Example 31 with the modification that EBs were plated on day 12. Neural progenitor cells were isolated from attached EBs at day 4 after plating according to the methods described in Example 51. In this example trypsin at a concentration of 0.05% was used. Cells were re-plated into a 6-cm well coated either with Poly-L-ornithine or 4 different concentrations of laminin. Coating was performed as described in Example 18 with the modification of the laminin concentrations. FIG. 54 shows attached EBs at day 4 after plating (upper row). The middle row shows NPCs 3 days after they have been isolated from attached EBs plated on 1, 5, 10 and 20 μg/ml laminin (from left to right). The lower row shows the same cells 7 days after plating. FIG. 55 shows an immunocytochemical staining of NPCs on day 3 on 10 and 20 μg/ml laminin and on day 7 on 1 and 5 μg/ml laminin. The staining was performed as described in Example 17 and cells were stained for TUJ-1, a neuronal marker to determine the effect of concentration of laminin on number of neurons. This example shows that NPCs can be re-plated on various concentrations of laminin with no influence on morphology or marker expression of attached neural/neuronal cells.

Example 54 Efficient Dissociation and Isolation of Neurons and Neural Progenitor Cells from EBs Generated and Cultured for 22 Days in mTeSR®1-F Osmolality 270 mOsm/kg or 340 mOsm/kg

EBs containing 2000 cells/EB were formed in AggreWell™800 from the human embryonic stem cell line H9 as described in Example 30 using mTeSR®1-F with an osmolality of 270 mOsm/kg or 340 mOsm/kg. EBs were released from the microwell plates at day 11 of culture and plated onto Poly-L-ornithine/Laminin coated dishes as described in Example 31. Neural progenitor cells were isolated from attached EBs at day 11 after plating according to the methods described in Example 53. FIGS. 56 and 57 show the attached EBs at day 11 after plating. There are not only NPCs present in the cultures but also mature neurons growing out from the attached EB structures formed and cultured in mTeSR®1-F with an osmolality of 270 mOsm/kg. There are only few NPCs and neurons observed in EBs formed and grown in mTeSR®1-F with an osmolality of 340 mOsm/kg. NPCs could only be generated from dissociated EBs grown in mTeSR®1-F with an osmolality of 270 mOsm/kg and not from mTeSR®1-F with an osmolality of 340 mOsm/kg. Immunocytochemistry (see Example 17) of re-plated cells at day 3 shows a mixture of NPCs and neurons as determined by Nestin and Sox1 or TUJ-1 expression respectively.

Example 55 Propagation of Neural Progenitor Cells for Several Passages Testing Different Dissociation Reagents and Surface Coatings

EBs containing 2000 or 10000 cells/EB were formed in AggreWell™800 from the human embryonic stem cell line H9 (p 36 and 41) as described in Example 30 using mTeSR®1-F with an osmolality of 270 mOsm/kg. EBs were released from the microwell plates and plated onto Poly-L-ornithine/Laminin coated dishes as described in Example 31. EBs containing 2000 cells were released from AggreWell at day 7 and EBs containing 5000 or 10000 cells were released on day 5 of culture in AggreWell. Neural progenitor cells were isolated from attached EBs at day 11 (for the 2000 cells/EB) or at day 7 (5000 and 10000 cells/EB) after plating according to the methods described in Example 52. FIG. 58 shows NPCs on day 4 (2000 cells/EB) or 6 (10000 cells/EB) of culture on Poly-L-ornithine/Laminin coated dishes (passage 1=P1). These NPCs were dissociated with either HBSS or TrypIE (Sigma, catalog number) and resulting cells were re-plated as secondary cultures on Poly-L-ornithine/Laminin or matrigel coated dishes (for 2000 or 10000 cells per EB respectively). The HBSS dissociation was performed by incubating the NPCs between 0.5 and 1 hour at room temperature and cell detachment was observed. The cells were triturated gently 5-10 times in the HBSS solution using a P-1000 pipette tip. Cells were centrifuged and the cell pellet dissociated as described in Example 52. For detaching NPCs using TrypIE, the methods of Examples 51 and 53 were used. FIG. 58 shows the passage 2=P2 cells on day 3 (2000 cells/EB) or day 1 (10000/cells per EB) which were plated at a density of 1.3×10⁵ cells/cm². Cells were treated at passage 3 (P3) with Trypsin (2000 cells/EB) (see Examples 51 and 53) or TrypIE (10000 cells/EB) on day 3 or 2 respectively. FIG. 58 shows P3 cells on day 3 or 4 respectively which are a total of 29 or 24 days post induction. The table in FIG. 59 summarizes the different time-points the splits were performed on cells originating from 2000 or 10000 cell containing EBs. Immunocytochemical staining (for method see Example 17) was performed for neural progenitor markers, showing Musashi, a neuronal precursor cell marker and ZO-1 expression, which is a marker for the lumen of the rosette (FIG. 59). NPCs are shown on p1d5 cells stained for Musashi and ZO-1 (originating from 2000 cells/EB). Rosettes can also be seen in p1d6 cells originating from 10000 cells/EB as shown by DAPI-cell staining. Mature neurons are mixed in with the NPCs (here shown with the marker TUJ-1). The results were obtained from cells cultured in mTeSR®1-F with an osmolality of 270 mOsm/kg but NPCs can also be cultured in mTeSR®1-F with an osmolality of 270 mOsm/kg supplemented with bFGF (10-20 ng/mL), EGF (10-20 ng/mL), B27 (1-2×) or N2A (1×).

This example shows that various dissociation agents can be used to dissociate NPCs for sub-culture over 3 passages and that these NPCs can be replated on different matrices.

Therefore neural rosette structures obtained by mechanical isolation and resulting NPCs re-plated as described in Example 15 or by any of the described dissociation methods in Examples 51 and 55 can be used to dissociate NPCs for further propagation over multiple passages. In summary, the previous 5 examples show that NPCs can be isolated from EBs harvested at different times from AggreWell™800, attached EBs displaying rosettes at different time-points and when attached EBs are cultured for different days. EBs can either be cultured in the AggreWell™ microwells for 24 hours or then released to be cultured in ULA plates or they can be left inside the microwells for up to 12 days. Also various sizes of EBs can be formed and NPCs can be isolated from those EBs with similar efficiencies. Furthermore, various dissociation reagents can be used to isolate NPCs and NPCs can be re-plated on different concentrations of laminin as well as on different surfaces. NPCs can be isolated during a time frame of 3 to 11 days after plating the EBs (this equals 11 to 22 days in total) and can be passaged several times without losing their ability to propagate as NPCs as well as spontaneously differentiate into neurons and astrocytes, see Example 57 and FIG. 66.

Example 56 Phenotypic and Molecular Characterization of Cells Within Neural Rosettes Generated in mTeSR®1-F with an Osmolality of 270 mOsm/kg and Non-Neural Cells Generated in mTeSR®1-F with an Osmolality of 340 mOsm/kg

In this example hESCs line H9 passage 63 was used. EBs containing 500 cells per EB were formed as described in Example 28 in AggreWell™400 and EBs were released after 5 days of culture in the microwells and attached to Poly-L-ornithine/laminin coated dishes as described in Example 29. Two media were used: mTeSR®1-F with an osmolality of 270 mOsm/kg and mTeSR®1-F with an osmolality of 340 mOsm/kg. To characterize neural progenitor cells present in neural rosettes of attached EBs, immunocytochemistry was performed as described in Example 17. Markers for NPCs that are described in literature were used. The earliest neural marker used was Pax6, followed by the later marker Sox1 and Nestin. Pax6 and Sox1 were expressed within rosettes of attached EBs formed in mTeSR®1-F with an osmolality of 270 mOsm/kg and weakly expressed or absent in EBs formed in mTeSR®1-F with an osmolality of 340 mOsm/kg as shown in FIG. 60. FIG. 61 shows co-expression of Pax6, Sox1 and Nestin marker expression in attached EBs from multiple experiments formed in mTeSR®1-F with an osmolality of 270 mOsm/kg. FIG. 62 shows co-expression of Pax6 and Sox1 with ZO-1. FIG. 62 also shows staining for BLBP, a marker of radial glia cells within rosette structures. FIG. 63 shows non-neural cells which emerge mainly in EBs formed and cultured in mTeSR®1-F with an osmolality of 340 mOsm/kg, which have no rosette structures and are “flat” in morphology (in this example H9 p52 hES cells were used). It is likely that these flat cells and the non-rosette structures are derived of mesoderm or endoderm lineage. These cells were scraped with a 200 P pipette tip by gently moving it back and forth in between attached EB colonies to obtain cells for qPCR. As a control, rosette structures were manually selected. Both cells types were transferred into a 1.5 mL Eppendorf tube and centrifuged at maximum speed for 1-2 minutes. RNA was extracted using Trizol (Invitrogen, catalog number 15596-018) and standard methods. Single round reverse transcriptase PCR was performed to generate cDNA copy (remaining RNA was digested using RNase) and cDNA was amplified using gene-specific primers and SybrGreen™ (GE Healthcare) using the manufacturer's protocols. Amplification of the desired products by SybrGreen incorporation was monitored using a 7900-HT machine (Applied Biosystems) and data analysis performed using standard programs (RQ Manager 1.2). The qPCR results are shown in FIG. 64 and demonstrate that Nestin and Sox1 transcripts are higher in “neural rosette cells” than in “non-neural (flat) cells”.

In summary, morphological, immunocytochemical characterization as well as FACS and qPCR for neural markers show that induction of neural ectoderm in mTeSR®1-F with an osmolality of 270 is efficient and NPCs can be isolated and propagated as well as differentiated into neurons and astrocytes. In comparison EBs formed in mTeSR®1-F with an osmolality of 340 mOsm/kg do not enrich for neural rosette structures and NPCs cannot be isolated. It is likely that osmolality of above 280 and 340 mOsm/kg enriches for non-ectodermal cells which have a different morphology than neural derived cells and are derived of mesoderm or endoderm lineage.

Example 57 Spontaneous Differentiation of Neural Progenitor Cells (NPCs) into Neurons and Astrocytes

Neural progenitor cells were passaged for several passages as described in Example 55 containing a mixture of NPCs, neurons and astrocytes. In this example EBs containing 2000 cells per EB were formed form hESC line H9 p36 in AggreWell™800 as described in Example 30. EBs were released and plated as described in Example 31 for 5 days. Next, attached cells were dissociated with HBSS as described in Example 52 and passaged. Cells were cultured for 8 days (Passage 1), dissociated with HBSS as described in Example 55 and passaged into the second passage. Cells were cultured for a further 5 days and then dissociated with TrypIE (third passage). FIG. 65 shows NPCs at passage 1 day 8 (p1d8), p2d2 and p3d3. In passage 1 and 2 mostly NPCs were observed, while in passage 3 sub-populations of neurons emerged spontaneously. For example, FIG. 66 shows cells expressing markers for gabaergic neurons. GFAP positive cells, indicating the presence of astrocytes can also be identified in spontaneously differentiation of NPCs.

Example 58 Efficient Induction of Neural Ectoderm in hPSCs Cultured in Adherent Culture in mTeSR®1-F with an Osmolality of 270 mOsm/kg With and Without Supplements

The human embryonic stem cell line H9 was passaged as single cells in culture for 4 passages between passage 51 to passage 55 (p51 to p55) as described in Example 21. 1.7×10⁵ cells were plated into a 6-well dish in mTeSR®1-F with an osmolality of 270 mOsm/kg alone or supplemented with 2% B27, 1% N2A or 1% B27 (Invitrogen, catalog number 17504-044). Matrigel and Poly-L-ornithine were used for adherent cultures of hPSCs prior and during neural induction. To a person skilled in the art, neural rosettes were apparent as early as 3 days after plating and induction. FIG. 67 shows induced rosette structures 7 days after plating them in induction medium (mTeSR®1-F with an osmolality of 270 mOsm/kg) onto matrigel.

While the present disclosure has been described with reference to what are presently considered to be the preferred examples, it is to be understood that the disclosure is not limited to the disclosed examples. To the contrary, the disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety.

TABLE 1 Target # of Clumps/Plate or Plate or Well Size Well 100 mm dish 2400 clumps  60 mm dish 1000 clumps wells in a 6-well dish  350 clumps

TABLE 2 Component Concentration as 1 × (mg/ml) Sodium Bicarbonate 0.544 L-glutamine 0.142 Human Holo-transferrin 0.0106 BSA 13.1 Thiamine HCl 0.0064 Reduced glutathione 1.942 L-ascorbic acid 0.32 L-alanine 0.0086 L-asparagine H₂0 1.456E−03 L-aspartic acid 1.292E−03 L-glutamic acid 1.428E−03 Glycine  7.28E−03 L-proline 1.116E−03 L-serine  1.02E−03 1000 × trace elements B 1.94 x 1000 × trace elements C 0.97 x Sodium Selenium  1.36E−06 Human Insulin  1.94E−03 Chemically Defined Lipids 1.942E−03 mL/mL 2Beta Mercapto ethanol 9.718E−06 NaCl for 260 mOsm/kg 0.027 NaCl for 270 mOsm/kg 0.33 NaCl for 290 mOsm/kg 0.95 NaCl for 320 mOsm/kg 1.87 NaCl for 340 mOsm/kg 2.48

TABLE 3 Required number of cells per well Desired AggreWell ™ 400 AggreWell ™ 800 number each well contains each well contains of cells approximately 1200 approximately 300 per EB microwells microwells 50   6 × 10⁴ cells — 100 1.2 × 10⁵ cells — 200 2.4 × 10⁵ cells — 500   6 × 10⁵ cells — 1,000 1.2 × 10⁶ cells 3.0 × 10⁵ cells 2,000 2.4 × 10⁶ cells 6.0 × 10⁵ cells 3,000 3.6 × 10⁶ cells 9.0 × 10⁵ cells 4,000 — 1.2 × 10⁶ cells 5,000 — 1.5 × 10⁶ cells 10,000 — 3.0 × 10⁶ cells 15,000 — 4.5 × 10⁶ cells 20,000 — 6.0 × 10⁶ cells

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The invention claimed is:
 1. A method of generating a population of ectodermal progenitor cells comprising: a) dissociating a culture of undifferentiated pluripotent stem cells; b) differentiating the dissociated undifferentiated pluripotent stem cells into a population of progenitor cells enriched for ectodermal fate by culturing the dissociated undifferentiated pluripotent stem cells from a) in suspension and/or in a microwell device in culture media with an osmolality of 260 to 280 mOsm/kg for at least 1 day; and c) dissociating the population of cells enriched for ectodermal fate generated in step b) and plating the cells onto coated culture dishes and culturing for at least 1 day in said culture media to produce the ectodermal progenitor cells as adhered cultures, wherein the cells in step b) are enriched for ectodermal fate when the percentage of colonies of the adhered cultures of step c) containing more than 50% by area rosettes is greater than the percentage of colonies of adhered cultures containing more than 50% by area rosettes when cultured in culture media with an osmolality outside of the range of 260 to 280 mOsm/kg.
 2. The method of claim 1, wherein culturing the dissociated undifferentiated cells in suspension and/or in the microwell device in b) comprises i) culturing the dissociated undifferentiated pluripotent stem cells from a) in the microwell device for about 24 hours to form aggregates and continuing the culture in the microwell device for more than 24 hours in the culture media followed by releasing the aggregates and adhering onto coated culture dishes and culturing in the culture media for at least 1 day; ii) culturing the dissociated undifferentiated pluripotent stem cells from a) in the culture media in the microwell device for about 24 hours to form aggregates, releasing the aggregates from the microwell device, followed by culturing the released aggregates in suspension in the culture media for at least 1 day, dissociating and adhering the aggregates onto coated culture dishes and culturing in the culture media for at least 1 day; or iii) culturing the dissociated undifferentiated pluripotent stem cells from a) in suspension in the culture media for at least 1 day followed by dissociating the cells and adhering onto coated culture dishes and culturing in the culture media for at least 1 day.
 3. The method of claim 2, wherein the aggregates comprise 500 to 20,000 cells.
 4. The method of claim 1, wherein the pluripotent stem cells are mammalian induced pluripotent stem cells or mammalian embryonic stem cells.
 5. The method of claim 4, wherein the pluripotent stem cells are human induced pluripotent stem cells or human embryonic stem cells.
 6. A method of maintaining single neural progenitor cells for at least 3 passages in culture media with an osmolality of 260-340 mOsm/kg comprising generating ectodermal progenitor cells according to the method of claim 1; dissociating the ectodermal progenitor cells from the adhered cultures; plating and culturing said progenitor cells for at least 1 day.
 7. The method of claim 6, wherein the cells are dissociated with a buffered solution comprising a Ca²⁺ and Mg²⁺ free buffer solution comprising 1×PBS or 1× Hank's Buffered Salt Solution with a pH range of pH 7.0 to pH 8.0.
 8. The method of claim 6, wherein the neural progenitor cells are further differentiated to form neurons, astrocytes and/or oligodendrocytes.
 9. A method of screening germ layer cells comprising (a) preparing a culture of ectodermal germ layer cells according to the method of claim 1; (b) treating the germ layer cells with a test agent or agents; and (c) subjecting the treated germ layer cells to analysis.
 10. The method of claim 1, wherein said culture media does not include GABA, pipecolic acid, bFGF, TGFβ1, and lithium chloride.
 11. The method of claim 1, wherein dissociating the population of cells enriched for ectodermal fate generated in step b) comprises applying a Ca²⁺ and Mg²⁺ free buffer solution comprising 1× PBS or 1× Hank's Buffered Salt Solution with a pH range of pH 7.0 to pH 8.0.
 12. The method of claim 1, wherein said culture media is serum-free.
 13. A method of generating a population of ectodermal progenitor cells comprising: a) dissociating a culture of undifferentiated pluripotent stem cells; b) differentiating the dissociated undifferentiated pluripotent stem cells into a population of progenitor cells enriched for ectodermal fate by culturing the dissociated undifferentiated pluripotent stem cells from a) in a monolayer culture in culture media with an osmolality of 270 to 320 mOsm/kg for at least 1 day; and c) dissociating the population of cells enriched for ectodermal fate generated in step b) and plating the cells onto coated culture dishes and culturing for at least 1 day in said culture media to produce the ectodermal progenitor cells as adhered cultures.
 14. The method of claim 13, wherein culturing the dissociated undifferentiated pluripotent stem cells in the monolayer culture in b) comprises adhering the dissociated undifferentiated pluripotent stem cells from a) onto coated culture dishes or feeders and culturing for at least 3 days in the culture media.
 15. The method of claim 13, wherein the pluripotent stem cells are mammalian induced pluripotent stem cells or mammalian embryonic stem cells.
 16. The method of claim 15, wherein the pluripotent stem cells are human induced pluripotent stem cells or human embryonic stem cells.
 17. The method of claim 13, wherein said culture media does not include GABA, pipecolic acid, bFGF, TGFβ1, and lithium chloride.
 18. The method of claim 13, wherein said culture media is serum-free. 